There are several options you might one to consider. Some that specifically focus on anger alone and some that examine anger along with other middos:
1) The Enemy Within
I highly recommend Rabbi Twersky z"l sefer entitled The Enemy Within by Mesorah Publications.
The sefer explores many middos such as anger, vanity, belief, worry/anxiety, diligence to name but a few.
The blurb reads as follows:
Though we are usually unaware of it, the lines of spiritual battle are drawn early in life and persist till our last day. In this intriguing book, the renowned Rabbi Abraham J. Twerski, M.D. delineates how the tactics of the yetzer hara are carefully tailored to each individual and how tenaciously it attempts to hold us in its grip.
And yet, Rabbi Twerski assures us, we each have the ability to triumph over temptation and live upright Jewish lives. Utilizing Torah wisdom and his deep insight into human psychology, he teaches us to galvanize our spiritual and emotional resources to battle the specific challenges inherent in today's lifestyle.
From common anxiety to oppressive depression, from the rush of daily obligations to the unique family tensions of the "sandwich generation," Rabbi Twerski discusses a broad range of modern ills and helps us feel confident that we can, in fact, strengthen our will and overcome them
2) Sefer Orchos Tzaddikim
Sefer Orchos Tzaddikim specifically looks at middos refinement and likewise has a chapter on anger. There is available an English translation version which is very good, and the older Feldheim version has a large chunk available on Google Books. Finally, it is also accessible online on Sefaria also with an English translation.
3) Anger: the Inner Teacher
Thirdly, there is Rabbi Zelig Pliskin's authoritative work on Anger entitled Anger: the Inner Teacher. The blurb there reads as follows:
Overcoming negative character traits is the essence and purpose of life” (Vilna Gaon). Anger is one of the most destructive traits. It can harm us and others spiritually, physically, emotionally, and socially. Anger, powerful and negative though it is, can also serve as our teacher (see Eruvin 65b). It shows us who we are, what is important to us, our level of self-mastery, and how we cope with adversity and frustration. We must learn from anger and, in the process, master not only it, but ourselves -- because we can. We are not doomed to repeat our tantrums and indignation, constantly and endlessly. We can change. But how? In Anger: The Inner Teacher, Rabbi Zelig Pliskin, a noted author and insightful counselor, presents a nine-step program to help us purge anger from ourselves. The author draws on Torah literature and his extensive counseling experience to build a comprehensive approach for coping with anger. This book is a practical guide offering underlying concepts and practical hands-on tools for decreasing and preventing anger. This step-by-step program is for anyone wishing to gain greater mastery over his other emotions. It also provides a useful model for those in the helping professions. As long as we are alive we can choose to correct the way we live. Anger is a natural human emotion. Refining and transcending it provides us with the opportunity to become the type of human being we wish tobe. Rabbi Pliskin has gained an international following as someone who sets his sights high but keeps his approach down-to-earth. Inspirational but practical, this book -- like its author -- is a realistic guide to a better, more fulfilling life.
4) Remove Anger from Your Heart: A Torah Guide to Patience, Tolerance, and Emotional Well Being
A final, fourth option you might want to consider which admittedly, I have never read but it looks very good is Remove Anger from Your Heart: A Torah Guide to Patience, Tolerance, and Emotional Well Being by Rav Avraham Tubolsky and Judaica Press. It is an English translation of the sefer הסר כעס מלבך and it would seem from the blurb that it was a favourite amongst Gedolei Yisroel and has a phenomenal roster of approbations. The blurb reads as follows:
Study the mussar series that the Steipler Gaon, Rav Shlomo Zalman Auerbach, Rav Shalom Schwadron and many other gedolim personally studied on a regular basis.
Rav Yehuda Zev Segal, the Manchester Rosh Yeshivah, zt"l, wrote:
"The books Remove Anger from Your Heart and Stay Away from Falsehood ... are truly very precious. I thank Hashem that I study them, and I gain greatly from them ... I would like to give copies of these books to my students, and I am sure that they will have tremendous benefits from them."
Rav Yaakov Yisrael Kanievsky, the Steipler Gaon, zt"l:
The Steipler loved the Sidras Tikkun Hamiddos books a great deal. Many visitors to his home testified that they found him immersed in these books, and members of his family relate that he studied them regularly. His son, Rav Chaim Kanievsky, shlit"a, recommends them and tells educators to use them in their classrooms.
Rav Shalom Schwadron, zt"l, wrote:
"How much you merited with these works cannot be measured or described. Congratulations, and may you merit added strength to produce works such as these for all the positive character traits ... Let me tell you one other matter. I, the small one, have committed this year during the Aseres Y mei Teshuvah that, im yirtzeh Hashem, this year I will study from one of your works every day!"
Rav Ovadia Yosef, zt"l, wrote:
"I bless him for his wonderful work ... and I encourage and strengthen him to continue this holy work, for it truly benefits many Jews. I know that, baruch Hashem, in many yeshivot they study his works, and they have been a great help to many rabbis and speakers!"
This book is a translation of Haser Ka'as Milibecha -- Remove Anger from Your Heart, a classic mussar work compiled by Rav Avraham Tubolsky, shlit"a.
The baalei mussar teach that the way to correct one's middos is through emotional learning and repetition of the words of our Sages. To that end, Rav Tubolsky collected and summarized sayings and lessons from our Sages throughout history, as well as anecdotes from the Talmud, practical suggestions to overcome anger, and stories about individuals who conquered their anger. The result is a work that has a powerful effect on the neshamah.
The most convincing testimony to the greatness of this book and series is the fact that gedolim past and present have frequently recommended it to others and learned from it regularly themselves.