Hello. More or less like this:
https://www.tp-link.com/pl/support/faq/417/ Log in to your main router and check what range its DHCP server assigns addresses from. Set the address of the second router (192.168.2.11 in the example, this will be your Archer C6) so that the first three octets of it are the same as the IP address of your main router, and the last number is
apart from the range of addresses assigned by the DHCP server of your main router.
Example - if your router is 192.168.0.1 and assigns addresses 192.168.0.100-192.168.0.200 then you can set as Archer's address, for example, 192.168.0.2 (assuming that no other device has been manually assigned this address) - it is in the same network as router, it will not conflict with the addresses given by DHCP.
