how do I add transmission fluid

Hello, You can add the transmission fluid through the dipstick tube. That is why it is so much larger than the oil dipstick tube, and there is no other access point to fill the transmission. Ensure you use the correct fluid as outlined in your owners manual. Lastly, repairing the leak will likely require that you replace the transmission fluid and filter as well, since the pan is likely at least one of the sources of your leak.