Exchange

That would be impossible.

You had fourteen days after the original purchase of the iPhone 7 (which was new six years ago) to have made such an exchange.

Apple will give you a trade allowance of $40 for a used iPhone 7 (if it is in excellent condition). This will likely be last year Apple will give you anything for such an old iPhone. And you certainly cannot buy a new iPhone 7. iPhone 7 was completely discontinued in 2019.