It's an old trick to clean out the injection system, BUT... it's not advisable for all vehicles, especially diesel engines with an aftertreatment system.
How much in what kind of fuel and why?
no way! never put transmission fluid in the fuel system. the car may catch on fire.
In the transmission.
You put the Transmission Fluid in the Transmission (fill point transmission drip stick tube)
The transmission will fail.
Low Transmission fluid
Buy a transmission funnel and pour the fluid in the dipstick tube.
In the transmission.
In the transmission!
The transmission fluid is added where you check it, on the toppish left (driver's) side of the transmission.
how do I put transmission fluid in a Saturn vue
For automatic transmission: remove transmission dipstick, put fluid in dipstick tube with funnel. be careful not to overfill.
Transmission fluid is always put in through the Tranny dipstick tube.