[egc]

Good catch from @mrjcd.

The problem seems not the OpenVPN server setup but your network setup.

If this OpenVPN router is connected with its WAN to your primary router then the subnet has to be different i.e. it should be 192.168.2.1

The static WAN is wrong, the default gateway and local DNS are wrong and who know what else is wrong.

My advice: reset the router to defaults.

After resetting connect to the router with a cable, reboot your client and you can find the router at 192.168.1.1.

After logging in, change the local IP address from 192.168.1.1 to 192.168.2.1
Save/Apply
Do not change anything else

After that reboot your client and you can reach the router at 192.168.2.1

Check if you have internet connection, setup wireless if you want to (check if it has a password set).

Alternatively consider setting the router up as a WAP:
https://wiki.dd-wrt.com/wiki/index.php/Wireless_access_point

Only after you setup the router correctly, setup the OpenVPN server according to the instructions from the guide.
If you decided to setup a WAP there is also a paragraph dedicated to running an OpenVPN server on a WAP

[Barcs2002]

Ok thanks very much for your help both, disabling WAN and turning it into an AP solved the problem!