@KillyKlamm
When the repeater connects to the main router, then its IP address will change according to the subnet that is used by the main router.
Therefore the C7's LAN address will now be 192.168.1.something.
To find out the exact IP address, log into the router whose signal you are repeating and look for a place where it shows the IP addresses of all client devices that are connected to it. In case the Archer C7 doesn't show up with the name "Archer C7", then you need to look for it by its MAC address (which you should find on the label on the underside of the C7). Once you have obtained the IP address you can use it to access the GUI of the Archer C7 again.
If all fails, then you can also factory-reset the C7 via its Reset button and then the C7 will boot up in router mode again with its default IP address of 192.168.0.1.
By the way, even if the C7 allows you to establish WDS connections to the same main router simultaneously via both 2.4 GHz and 5 GHz, it is not recommended to do that. (although I am not sure what exactly is going to happen if both bands are connected)
The bands and SSIDs on which the C7 will "repeat" the wireless signals are still controlled via the Network -> Wireless menu.