Trying to setup a guest ssid in my elementary school. Below is how the ISP has our firewall configured. 
 
0/3                         1x.2xx.2xx.1/22                Internal Wireless             VLAN 35 Tagged
0/3.1007                1x.2xx.9x.0/23                   Guest Wireless                  VLAN 1007 Tagged
 
I am new to this process and would like to figure it out instead of contacting my vendor to set it up.  
I assumed I would use NAT Mode but how do I configure firewall settings to pull from my IP pool setup by the ISP instead of this one? (10.0.0.0/8)
NAT mode: Use Meraki DHCP
Clients receive IP addresses in an isolated 10.0.0.0/8 network. Clients cannot communicate with each other, but they may communicate with devices on the wired LAN if the SSID firewall settings permit.