New Firmware Fritzbox and Wireguard

sorry for my bad english, i use google translator!
The new laboratory firmware of the Fritzbox 7590 finally allows Wireguard Server and I would like to create a profile for my SPITZ (for Camping), the Fritzbox asks for the subnet when creating it, what should I enter here? I’m sorry, so far I’ve used a CRETA as Wireguard server, I didn’t have to enter anything like that and it worked immediately! But I would like to remove the CRETA from the Fritzbox and do everything via the Fritzbox!

you can use 10.0.8.1,
netmask 255.255.255.0
This is what we used by default.

great thank you so much