It’s great that there is one office of Vietnam embassy in Minsk, Belarus. It means that your visa issuance, legalization requests can be processed more conveniently than those in countries without an embassy/consulate of Vietnam. You can find the contact details of this embassy below:

Regarding visa for Vietnam, in addition to embassy visa, citizens and residents of Belarus has an alternative of getting a visa on arrival. You can see their brief below:

• Get embassy visa: the applicants need to contact the Vietnam embassy in Belarus for visa application and processing;
• Get visa on arrival (also known as visa at the airport): the applicants will submit an online application form for visa approval letter issued by the Vietnam Immigration Department, and finally get visa stamped upon arrival at Vietnam airport. You can see how VOA works.

For details, you may also read:

• How to get Vietnam visa for Belarus citizens