Same place you check the level.
Dexron 3
6
Thru dipstick tube
I'm assuming you mean a Ford F-350, which you fill through the dipstick tube.
Simply pour the fluid into the tube that you removed the dip stick from for checking the level in the transmission. DO NOT overfill the transmission.
5 QTS.
dexron II
Must be transmission fluid leak somewhere, and it's getting fluid on the exhaust. I'd be looking at the lines to the cooler first.
350 Engines dont have transmission fluid. The Transmission does. Start the engine, leave the trans in Park, pull the dipstick and look at it. fill to full mark when the engine is fully warned up
If the tranny is empty you need about 12 qts. to fill it.
A typical Turbo 350 transmission fill tube is the same tube that holds the transmission dip stick. It would be located in back of the engine, a little to the passenger side.
You should never add transmission fluid to a Chevrolet 350 engine. You can add transmission fluid to the transmission through the transmission dipstick holder.