@DonThomas
Welcome to the community!
It sounds like there are a couple of ways you can approach this:
First, if you change the password of your main router (assuming this is the Deco X20) so the TV can automatically connect, there's a chance all of your wireless devices will need to reconnect to the network using the changed password.
Alternatively, you should be able to enter the TV's network settings to forget/clear the existing network profile and reconnect it to the Deco X20 using the current Wi-Fi name and password. I would recommend trying this first since it would only involve a quick settings adjustment on the TV, and not a network-wide change.