How to use GPON in Bridge mode and OpenWrt router as main?


Total openwrt and networking noob here.

ISP provided Nokia G-2425G GPON router however I would like to use my Mi 3G (Openwrt) router as my main and use the ISP provided as just a gateway or in bridge mode.

I am totally lost here on how to configure this setting or what tutorial to follow.

Please help me guide in the right step.

That has nothing to do with OpenWrt. Ask your ISP and/or search for the admin guide for your ONT.
In most cases you will need to configure bridging [on the ONT] between ISP VLAN and one of the Ethernet ports.