Using Archer C6U as a wifi client

I want to create a very simple setup with my Archer C6U but somehow not able to do it.

All I want to have Archer C6U connect over WiFi to my modem(fibre ISP provided) and then connect my TV to LAN port of tp link router. By this setup I want use internet from modem on my tv.

Any guise for it.

There are a few ways to handle this, as it depends on what your goals are.

If the network behind the C6U doesn't need to be the same as the upstream network, a simple routed mode operation with the C6U connecting as a wifi client (i.e. wwan) is the easiest to configure.

But if your intent is to make this a wireless -> wired bridge, you need to use relayd:

https://openwrt.org/docs/guide-user/network/wifi/relay_configuration