Access LAN via WAN

Hi All,

I’m looking for a bit of help configuring a network, it’s a bit of an unusual setup.

There is a master network 10.0.0.XXX, this network has a WAN to the Internet via 5G

On the LAN side of this network there are 3 networks, these connect via their WAN ports, all networks are on the same Peplink BR-1 MAX 5G routers, including the master network. 20.0.0.XXX, 30.0.0.XXX, 40.0.0.XXX

I need the entire subnet of each network to be accessible from the master network (10.0.0.XXX)

I presume I need to open access through the NAT and broadcast to the master network how to route to each sub network, does anyone have any experience with this?

Opening access to one or more spacific IP seems fairly straightforward, but, the entire subnet seems more complicated

Any help would be hugely appreciated

Many thanks,

Jon