I assume that your internet is DSL, connected via the Thomson modem's DSL port, and the TP-Link is a Wi-Fi NAT router.
To add the TP-Link Wi-Fi router to the Thomson modem, and simply use it for wireless, you can connect it as an Access Point. That means use one of the LAN ports on the Thomson, and, one of the LAN ports on the TP-Link.
Note that you may connect to the TP-Link via Ethernet cable first, and change its mode from "nat router" to "access point", and it's IP address to something in the range that your modem is serving, i.e. 192.168.1.*. That way, you will be able to access it once it is connected to the Thomson modem easily via that static IP.
There is more info on how to set this up on the main site, here:
https://www.speedguide.net/articles/...ess-point-2556
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