Tibetans traditionally fold dumplings this way for Mothuk (Momos in soup), where they are boiled in broth rather than being steamed.
Place the wrapper in your left hand (or reverse these instructions if you are left-handed). Using your right hand, spoon a tablespoon of filling into the centre and pinch together the top and bottom of the wrapper at the right-hand end. Then, pushing the filling inside the wrapper with your left thumb, press together the sides of the wrapper first with the index finger of your right hand, then with the thumb, all the way along. Seal the momo with a final pinch.