@cdasteve 

Hi, welcome to the community.

On the Deco APP, you could directly add a new main Deco to the current network, and after setup, the previous internet configuration and Wi-Fi settings remain unchanged.

For more details, please have a look at this link:

How to Set up the Satellite Deco or a new Deco to be the Main Deco

PS: Since the new Wi-Fi 6 and above models in the same pack are pre-configured, once the first Deco X90 is added to the Mesh network, the second Deco X90 will automatically join the network after powering up.

Thank you very much.

best regards.