TP-Link Archer C6 v2 as network extended

I used TP-Link Archer C6 v2 as wifi extender before, it;s connecte to my man router with wifi , but it;s not stable

can i connect it to main router with WAN eth port then connect to lan ports & wifi with same subnet?
i tried to use dump AP senario but i cannot access computers connected to lan ports

then you must have done something wrong, dumb AP is exactly what you need.

you could have forgot to reassign the wan port, or try one of the lan ports instead.

I dont do that, you are right
but it's not in documentation , appreciate your help