I want to find out how to bring back money from vietnam and how to exchang from vietnamese dong to us dollar

I don't quite understand the question - are you visiting and bringing money with you? Did you sell something and are bringing the money with you?

You exchange currency at International banks.

How much money are you bringing back, on large amounts, you deposit it in the bank in viewtnam and wire transfer it to your bank in the US

Ifyou are talking actual cash, you keep it in your pocket and merely exchange it at any local exchange store, or at many larger banks