TPLINK tlmr-3220V as a bridge for LAN and WIFI

Hi, i have a complicated lan/wifi setup and want to fix it:

1/ Main router (optic line from ISP) broadcasting wifi SSID "xxx"
2/ Device TPLINK TLMR-3220V2-> acting as a AP router -> Wan port connected to Main router, broadcasting wifi SSID "xxx", ip from dhcp in subnet

i want to setup this TPLINK as a bridge for LAN and WIFI and as a result all connected clients via LAN or WIFI are operating in the original subnet. Current firmware on the router doesn not allow to choose i can only setup a WBS bridge (but i want to use WAN port not wifi from router one (no range)
is it possible somehow with openwrt firmware?

is this a typo ?
if you meant ISPs 192.168.0 subnet, configure it as dumb AP

the 3220 is a 4/32 device, with very limited resources.