。
Could you trade seats with me?
Literal
I [with-と] seat [object-を] exchange-[for-me-ませんか].
替わる ('to change, swap') takes と for the partner in the swap. 席を替わる literally 'to swap seats' — the seat is the object of swap, the other person is the co-participant. ~てくれませんか is the polite request form. A common scenario on trains/planes.