How to configure openvpn server firewall rules

Hi, i would like to set openvpn server on my router (OpenWrt [21.02.3])
I do this:
and evrything is ok
but now I want to do some change in firewall rules (for example restricted acces to only one addres in lan).
is any file where can I do (experimential) changes??
Command line is not so good for beginners :slight_smile: