@Phildec Yes, that would be a problem since these are different subnets. Change the RE550 IP address to 192.168.1.254 and make sure that its DHCP server is set to Auto or OFF.

@Mercy23_KN Here's the guide for resetting router management password.

@Patrick33 If you're using Windows OS make sure that the new network adapter connection is of a type Private Network.

@elijamiesont Your issue comes from the fact that you're behind a CG-NAT. The only thing you can do is to contact your ISP and ask for an option to have your public IP address on your router's WAN...

@Phildec Use a web browser on a laptop for configuring RE550. The default IP address of the RE is 192.168.0.254. If your router LAN is in another subnet use the http://tplinkrepeater.net while...

@sparks79 Usually those are cabling issues which are resolved by changing the ethernet cable. If you have other devices connected to the switch and they are OK, change the printer cable.