@Frobozz 

Welcome to the community.

The “Create a Network” option in the Deco app is intended for setting up an entirely new, independent Deco mesh system (for example, at a different location or with separate hardware). That is why the app asks for the main unit to be in setup mode (blinking blue LED). You do not need to do this—and you should not reset your existing system—to add an extra SSID on your current mesh.

Your Deco BE63 already supports multiple SSIDs on the same system. Here is how to create one reserved for the 5 GHz / 6 GHz bands:

Use the Guest Network (easiest for a dedicated 5/6 GHz SSID)

Open the Deco app → More → Guest Network.
Turn on Guest Network.
Set a unique SSID and password.
Tap Advanced (or the band/settings section).
Select only the 5 GHz and/or 6 GHz bands.
Save.

Guest networks are isolated from your main network by default (in Router mode), which is often useful.

Enable / configure the MLO network (good for high-performance 5 + 6 GHz)

Go to Wi-Fi Settings.
Look for the Multi-Link Operation (MLO) option and enable it if it is not already on.
It creates its own SSID (often with an “_MLO” suffix that you can rename).
In the MLO settings you can usually disable the 2.4 GHz band so the SSID uses only 5 GHz + 6 GHz.
Note: MLO works best with Wi-Fi 7 clients and typically requires WPA3.

Check / adjust the separate 6 GHz SSID

Many BE63 setups already broadcast a dedicated 6 GHz SSID (often named something like YourNetwork_6GHz).
You can rename it and use it as-is, or combine it with the options above.

Additional notes

Your existing IoT network is already set up and is typically best left focused on 2.4 GHz for compatibility with smart devices.
Band selection and advanced options can vary slightly by exact firmware version, so make sure your Decos are updated (More → System → Update Deco).
After creating the new SSID, devices that support 5/6 GHz can simply connect to it. You can also use the client “Connection Preference” setting in the app to force specific devices onto preferred bands if needed.

This approach keeps your current three-node wired-backhaul system intact and adds the extra network you want without any factory reset.

If the suggestions above do not address your issue, please reply back to this post.

Thanks