Access between two domains


I have a router from my ISP that connects to the Internet, supplies the landline telephones and is connected to all wired devices. I would now like to use my GL-AXT1800 to replace the ISP router's outdated wifi.
Since I want to have a normal Wifi and a guest Wifi, the GL-AXT1800 is set as a router in network mode.
As I have 2 domains (devices on the ISP router are in 192.168.2.x and the devices on the GL-AXT1800 are in 192.168.8.x), I cannot currently ping devices in the Wifi from my wired PC and the other way around.
Is there any way that I can access the devices in the other domain without changing the network mode to access point (because I will lose the guest wifi)?

As I understand, you shall set the port forwarding on the AXT1800 if you want to access the LAN devices from the WAN side.

You can share your network topology and we shall advise.

You mean like this?

Thanks for it.

You cannot ping 192.168.8.x from 192.168.2.x by default.
You shall make it with port forwarding.

May I know you actual application that you need to access the LAN devices of AXT1800.
If just a few services, then port forwarding would be fine.
If too many services, it would not be a good way to make it

there are very diverse use cases. whether I want to access the NAS from my smartphone or the smarthome devices from my PC. Could port forwarding also be set for port ranges and just forwarding every port?

Not only support port ranges but also special one custom port.