Decode string with hex character codes to UTF-8 characters
Are you willing to use % instead of =?

If so Uri.UnescapeDataString shall be sufficient. if not you can always Replace("=", "%") and use UnescapeDataString anyway.

Uri.UnescapeDataString("Test =64 =C2=AE =E1=A6=92 test".Replace("=", "%"))
//Test d ® ᦒ test