Apple App Store won't let me sign out

I recently updated my Apple ID, but the App Store on my Mac mini is not allowing me to change my previous Apple ID email address to the new one. It is locked on the old email address and only allows me to enter a password (the entry field for the Apple ID is greyed out, with the out of date email locked in), which is now tied to the new email address and account. When I enter the correct password it says it is wrong because it doesn't match the old Apple ID. When I take steps to reset the password, it sends it to my new Apple ID account because it is recognized everywhere else, just not in the App Store. I'm not able to make updates to any apps on my desktop because it keeps prompting me to sign in using my old Apple ID and it is quite frustrating. 😟

I am running on a Mac mimi (Late 2012) and macOS Sierra 10.12.16.