1987 4runner transfer case fluid change

[02runner4]

I have a 1987 4runner with auto tranny. I'm not quite sure how to change the transfer case fluid. The owner's manual says that I just need to add the fluid when it's low with ATF. The picture shows only one filler hole. I want to drain and refill the transfer case. Also, I see two drain plugs for transmission fluid. There is a big transmission pan, and a small transmission pan behind it. I'm confused.