Yes you can.
In the transmission.
You have to have the dealership do it, because you cant simply drain it and put new stuff in. They have a machine that simultaneously drains it and puts new stuff in.
You pour it in a funnel connected to the check fluid tube. You will need to get a transmission fluid funnel.
Thru the transmission dipstick tube.
Through the dipstick tube
It is important to maintain the fluid levels in a car, and it is important to put the right type of fluids in the car as well. A 1989 Chevy Pick up uses Dexron III transmission fluid.
as long as it is an automatic transmission, you put ATF in
Thru the dipstick tube.
Through the dipstick tube
Dexron II or any other transmission fluid for GM vehicles.
In the tube that holds trans dipstick.