How do I add fluid

Through the transmission dipstick opening, using a long-neck funnel. Don't overfill. It should not be filled past the top full line, when the transmission is at normal operating temperature and in Park.

Then again, some don't have dip stick tubes anymore. Could even be a manual trans the poster is asking about.
How about checking here first.
https://www.askmehelpdesk.com/cars-trucks/when-asking-about-your-vehicle-303903.html