trying to add gear oil to a 1999 toyota tercel on 1999 Toyota Tercel

hi we just recently had the transmisssion repaired in my 99 toyota tercel... we were told that we should add some gear oil to the car... and i have no idea where i add it, could someone help me with directions on where to put it and how to get there and such?

Asked by for the 1999 Toyota Tercel
Filler plug is a 22mm plug about half way up on the transmission housing at the radiator side of the transmission.