How to connect two routers with OpenWRT in one network?

Question

DHCP

Help.
There are two TP-Link routers with OpenWRT 18.06. Now they work according to the scheme:
Provider - [WAN] Router1 (wifi1) [LAN1] - [WAN] Router2 (wifi2)
Accordingly, there are two different Wi-Fi in the house and there is no connection between devices from different networks.
I want to make sure that DHCP is only on the first router, and the second one (both itself and the device) receives IP from the first one. But I can not master the web interface in any way. I turn off the second DHCP - I lose access to the router.
Google suggests that you need to dig in the direction of dhcp relay / bridge, and somewhere else.,, I can not master it.
Give instructions on what to do. It's already evening, the head does not think.
Preferably with an indication on which tab which checkbox to put :)