So you want a client bridge and not a router, so see if you can turn routing off and connect the it to your existing WLAN and then preferably bridge the wireless and wired interfaces. All this can be done with openwrt.org but I don't know if your router is supported
The wireless radio UCI configuration is located in /etc/config/wireless. If the device has ethernet ports, the wireless is turned OFF by default. You can turn it on in /etc/config/wireless by changing option disabled '1' to option disabled '0' (commenting out the line or removing it is sufficient). Configuration of a wifi client in openWrt. For working with wifi in openWrt there is a script /sbin/wifi. The file /etc/config/wireless is responsible for wifi configuration. The the configuration file can be created by default having run the following: wifi detect > /etc/config/wireless. It will look as follows: Oct 22, 2013 · Configuring OpenWrt as a Routed Wireless Client This page contains an overview on how to configure a LinkSys WRT54GS running OpenWrt as a routed wireless client router. Introductory Information Firstly, be sure to have a look at Matt Kemner's guide to turning the Linksys WRT54G / WRT54GS into an AP-client and routing node. It provides a concise Dec 18, 2012 · Setting up Wireless client mode in OpenWrt on TP-Link TL-WR1043ND. Comedians in Cars Getting Coffee: "Just Tell Him You’re The President” (Season 7, Episode 1) - Duration: 19:16. blacktreetv Mar 17, 2010 · I already have two Linux-compatible wireless routers, an Asus WL-500G and a Fonera. Both running OpenWRT. If my routers had Broadcom wireless chipsets then this task would be easy. Thanks to driver support, OpenWRT can automatically bridge network segments through a wireless client (at least on 2.4 kernels, not sure about 2.6.) I'm trying to set up a "wireless switch" since some of my device have no wlan adapter. I'm using an Asus RT-AC51U flashed with openwrt. Following this guidance I was able to connect the Router as a client to our wlan and also connect a device via cable (using relayd). Unfortunately the speed of the connection is to slow for proper use.
Luci (openwrt) wifi bridge client - how to configure
Flyspray::OpenWrt/LEDE Project: Tasklist
Difference Between Client Bridge/Wireless Repeater Modes
May 29, 2018 How to Configure OpenWRT Wifi Router WISP / AP+Client Mode