What should I do with the profit I received from a usurious bank; should I donate it as charity or am I obligated to return it even if I do not currently possess it or am in need of it?

Contributing to usurious banks and receiving interest on their shares is forbidden (haram), and its perpetrator is at war with Allah. The fundamental rule concerning such interest is that it is impermissible to benefit from it, and it must be spent on the general welfare of Muslims. Since you spent these funds for your private benefit, despite knowing it was forbidden, you have committed an additional sin. You must sincerely repent, and you are not required to spend other funds in their place.