How does a native English speaker say "You may return to your seat" in polite way? I've ever heard my lecturer said, "you may return to your expected chair." But I'm not sure about the "expected" part, maybe I heard it wrong.
I'm not going to claim to be a native English speaker (although I speak and write in English much better than my own mother tongue), but this is a line I've often heard being used:
Kindly return to your seat.
Please return to your seat.
The statement you wrote,
You may return to your expected chair.
also appears to be grammatically right, but as commented earlier, it's a very odd expression...