1997 Cadillac Catera the transmission light comes on after

Transmission problem
1997 Cadillac Catera 6 cyl Two Wheel Drive Automatic 90k miles

After the light comes on I can turn it off and start it again and the light will be off again. I just got this car so I don't know much about it. I thought maybe it might just be the tranny filter. I bought the filter kit. Now I can't find where you fill the tranny after you replace the filter. Thers no dipstick. I hope its not gonna be an expensive repair. Can you give me some advise as to what I shoud do here. Thank you very much. Tim