AC78U as OpenVPN client with routing into internal network?

Hey there,

I have got the following problem:

I have got an OpenVPN server on the internet (hosted by my self - changes are possible) and successfully connected my router (ASUS RT-AC87U, asuswrt-merlin 384.13_10 ) as a client. Furthermore, I connected my phone as a client. Now I want to connect to Raspberry Pi in my local network.
local network: 192.168.1.0
vpn network: 192.168.255.0

I do not want to route any traffic from local network through vpn, except route back a vpn client which is...

AC78U as OpenVPN client with routing into internal network?