How to access Different Subnet Router Lan => Peplink WAN

Hey there,
im facing a problem with accessing devices on Peplink dhcp WAN when using vpn on internet router.
Im using 2x Internetrouters on a Peplink Balance 20.
Both of them are connected to the internet via WAN PORT on the device itself.
I have to connect them like this because the internet routerss are from provider.
Both of these routers are connected via LAN to WAN 1 and WAN 2 on Peplink!
WAN 1 is the Port which is configured as IP forwarding!
WAN 2 is only for load balancing for specific upstreams!
Peplink acts as a DHCP Server Serving 192.168.1.x
The Internetrouter on WAN 1 is in Subnet 192.168.0.x
Both of them act fine when using locally !
Internetrouter 1 which is connecte to WAN 1 also offers WIFI for clients !
This works great - and I can access devices on Peplink 192.168.1.x when connected to wifi 192.168.0.x - as a static route is configured to peplink lan port on the internet router!

But when im connected via VPN to this internet router I cant connect to devices on 192.168.1.x (WAN 1) Peplinkā€¦
I dont know why and I dont know how to fix - i tried using a NAT port forwarding but I cant map any network drives like this.

Can anyone help me on this?