automatic transmission drain plug

You do not have a drain plug in this pan. Take a look at the attachment below and that will show that it says when remove the valve body that you need loosen the pan and allow the fluid to drain.

Here is a guide that will help with general info if you or others in the future need it:

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

Below is the process. Please let us know if you have other questions. Thanks