What about those that want to get from the level of Rasha to Beinoni, is there a book for that?
It is called Sefer shel Beinini and the few things I've read in it seem to be instructions directed for and addressed to the Beinini.
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The Tanya uses the word rasha and beinoni in different ways than most of us. When this is understood, it becomes clearer that the Tanya actually is a manual for how to become a beinoni.
In the language of the Tanya, the beinoni is at a very high level but a realistic target (from this introduction to Tanya)
a person who exercises complete self-control and never commits a sin knowingly in any of the three areas of human activity: thought, speech and deed. [... the author] insists that this ideal personality is within grasp of the average individual, although not without constant effort and vigilance. The underlying doctrine here is that man is essentially and inherently a moral being.
The rasha of the Tanya is not all bad either (from chapter 11)
There is also the person in whom the wickedness prevails more strongly, and all three garments of evil clothe themselves in him, causing him to commit more heinous and frequent sins. But intermittently he suffers remorse, and thoughts of repentance enter his mind, from the quality of good that is in his soul, that gathers strength now and then. However, he has not enough strength to vanquish the evil so as to rid himself entirely of his sins and be as one who confesses and abandons [his evil ways, once and for all]. Concerning such a person, the Rabbis, of blessed memory, have said, “The wicked are full of remorse.” These represent the majority of the wicked, in whose soul still lingers some good.
The Tanya's audience was large and varied and aimed to help all reach their potential (from here)
Most of [R Shneur Zalman's followers], undoubtedly, were simple folk and laymen. But there were also many students of the Talmud, and philosophically inclined young men, who, like himself in his teens, sought a new way of life and new outlets for their intellectual as well as spiritual drives. The consideration of such a [varied] audience largely determined the form and style of the book.
My recommendation for someone wanting to learn Tanya is to find a good commentary, or a simplified version of it. I personally got a lot out of GPS for the Soul by R Nadav Cohen which is an explanation and simplification of many of Tanya's concepts, in a language modernized for our day and age. See also here.
No, the Tanya is meant for the average person who is not a tzadik and who has the potential to be a bononi. The reason that the Tanya and the first part of Tanya are referred to as "sefer Shel benonim" (the book of the in between each) is to help each of us attain the rank of being a benonim as the parable in the talmudic quoted in Tanya as being the longer shorter route to acheiving this goal.