Foreingers who live in Viet Nam and want to exchange international driving license into Vietnamese one can come to Vietnamese Transport Departments to do this procedure.
Here are exact addresses of some Vietnamese Transport Departments:
Ho Chi Minh City:
252 Ly Chinh Thang, Ward 9, D3, Ho Chi Minh city.
16 Cao Ba Quat, Ba Dinh District, Ha Noi.
To learn how to do the procedure you can refer more information here.