Automatic transmission fluid overfill, how do I drain some out?

Sure, it is not too bad to let the excess fluid out just loosen the transmission fluid pan and it will start leaking. Use a fluid catch basin to catch the fluid. You may want to replace the gasket and filter as long as you are there. Also, I have seen people use a fluid extractor with a thin tube and feed it down the dip stick tube and suck it out that way as well.

This guide can help:

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Check out the images (below). Let us know if you need anything else.