i don't think you can sorry
with a dipstick
You pour it in a funnel connected to the check fluid tube. You will need to get a transmission fluid funnel.
The transmission fluid capacity for a 1991 S10 5 speed manual transmission is approximately 3 quarts. This can be purchased at any auto parts store.
The 1991 Chevy or GMC S10/S15 with a 5-speed manual transmission typically uses GM's manual transmission fluid, often referred to as GM Synchromesh or an equivalent fluid. The capacity for the transmission is approximately 2.5 to 3 quarts, depending on the specific model and configuration. Always check the owner's manual or service manual for exact specifications.
Check the transmission dipstick, it is written on the stick what fluid to use.
There is a plug on the side of the tranny. take it out. If fluid runs out, put the plug back in the hole and get on with life. If no fluid runs out, check your manual for what transmission fluid to use. Fill it till it runs out at the plug a bit. Be sure to use the transmission fluid recommended for Chevy S10 5 speed manual transmissions.
Assuming this is an automatic transmission, you can add ATF through the transmission dipstick tube. The dipstick itself will tell you what type of fluid to add.
Dextron 3 Transmission fluid
5 spd you need 2.9 qts and recommend GM syncromesh
Have the vehicle towed to a transmission shop to be flushed and serviced.
The correct automatic transmission fluid for that vehicle is written on the transmission dipstick.
There isn't a transmission fluid reservoir on an 86 S10 pickup. The transmission fluid is held in the transmission itself.