Access to isp router behind openvpn server

[Pca]

Hi, I'm new around here.

I have this configuration:
Router ISP: Bridge mode (192.168.0.1)

Router ASUS AC68U :
Firmware: Asuswrt-Merlin 834.13 (Thank you Merlin)
Minimal configuration
wan ip: 192.168.0.2
lan ip: 192.168.1.1
My ISP uses pppoe

Everything works correctly, except that I would like to access the isp router through the openvpn server of my ac68u.

-From the local network I can access to 192.168.0.1
-From outside I can connect to my vpn server and see all the equipments that are in the network 192.168.1.0 except my isp router.

I have tried several configurations but without result.

I hope someone can help me.

Thanks to all