equipment credit

I purchased a iphone 14 from t-mobile. I wanted the 16 plus however, i had a $400 down payment and i didn't have it. I went for the 14 because i needed a phone immediately (mine was stolen). i figured i would give the 14 to my daughter and then get the 16 plus on payday. Well i checked today and my duwn payment is 750 now.My question is that if i were to just do a return , will my credit limit increase back to the original amount making the down payment $400 instead of 750? Does anyone have experience with this