Using WRT router as wifi client

Netgear DGN3500
Installed openwrt-19.07.7-lantiq-xway-netgear_dgn3500-squashfs-factory.img
Seems OK.
I have used DD-WRT before, but not OpenWRT.

I have a wireless router connected to DSL in another room (the "master").
I want to use the DGN as a wireless client to that, and attach devices to it -- a desktop PC and a laser printer -- via ethernet. I don't need, or want, to create or extend the wifi, want the other router to do all the DHCP.

I've stumbled around the GUI and got it working, to the extent I can plug a PC into to it and go online.
But my PC gets a 192.168.* IP, and the master router is on 10.0.*.
I want the printer to be accessible to devices connected to the master. Also to use Airdroid with my phone, etc.
So I presume I need to turn off DHCP, so each device I plug into the DGN will be given a 10.0 IP. How do I do that, and is there anything else I've missed?