@jmwifi This resolved, but I'm not 100 sure how. I believe I rebooted the deco and it used the new password after that.

I had forgotten my TPLink Password and was unable to login into the Deco M4 Web Interface. I changed my password on the android app and re-logged into the app. But this new password does not work...

When I select update Deco from the Android, the app spins for a while and returns with an error message. Unable to Check for Update.