Can I replace a M3 chip with a M5 chip on a MacBook Air 2024?

No.

What you could do – once new Mac notebooks with M5 chips are available – is to convert that M3 MacBook Air into cash (by selling it) or trade-in credit (by trading it in to Apple). That would not cover the cost of a new machine, but might help to make buying a new machine more affordable.

Currently, the only Mac notebook with the M5 chip is the 14" M5 MacBook Pro. Apple is not using M5 processors in the MacBook Air yet, although it is reasonable to assume that they will be updating the MacBook Air line with newer processors at some future unannounced date.

No, that's not possible: Apple's chips are an integral part of the motherboard and cannot be replaced by users.