Convert C# string to win-1251

Question

I have the following string:

string str = "Здравей!";

I have to pass it to a printer to print it. The printer method to print is datecs_test.PrintTaggedText(str); But on print I don't get the same string content but some strange symbols. They told me that before I pass str to datecs_test.PrintTaggedText(str); I have to convert str to win-1251. But all solutions I find doesn't seem to work.