Im trying to find a way to increment a certain variable until a condition is meet. Can someone help me with this?

Ive attached both files that are needed to run the code, everything works ok. If you look at the file, its a code that models a rocket engine booster stage. 'PR_1' is the model, and 'booster stage' is the engine selction of various types. My goal is to increment the chamber pressure, P_c, until a thrust requirment is meet; thrust avalible, F_ava is greater or equal to thrust required, F_req.