@paddepal 

As per your description, the two Archer C6 V3.20 are connected to the main gateway router with Ethernet cables via LAN, and both are working as access points. If that's the case, you can try to set up the same SSID and wireless security, password on both access points to check if you can roam properly.

Or you can try to set up the second Archer C6 V3.20 as a repeater by connecting it to the first by Wi-Fi, below are the instructions to achieve that:

https://www.tp-link.com/support/faq/1555/