If someone doesn't daven shemoneh esrei for certain reasons, he is able to make it up by davening two shemoneh esreis at the next davening ('tashlumin). The second one is the exact same as the first, except in the case of tashlumin motzei Shabbat, where atah chonantanu is not said the second time.
In an ordinary case, if someone forgets atah chonantanu, they don't repeat shemoneh esrei, because they can just say havdalah later.
So, here, what if someone forgets mincha Shabbat afternoon and has to say tashlumin at maariv. Then, they forgot atah chonantanu in the first (maariv) shemoneh esrei. Should they say it in the tashlumin (mincha) shemoneh esrei, even though it wouldn't normally be said then?