Need help connecting to another router

Hey everyone, I recently bought a GL 750v2 and I have a ATT SIM card in it. I pastor a church and the internet in the building we rent is terrible. So this is my solution. The wifi works great no issues. But I would like to connect the 750v2 to another router that’s stronger and has other LAN ports to connect other devices. Is that possible? if so how? because I tried and can’t figure it out. The other thing, when I connect my Mac mini directly to the 750v2 it shows connect via ethernet but no internet. Im pretty much a newb to this, any help would be greatly appreciated. Thank you in advance.

You want to connect X750 to another router via cable?

That is pretty simple.

Connect X750’s WAN port to another router’s LAN por.t