hello @Bob5
You have two options to apply a static IP to the GX50.
The Loacal Status Page as mentioned. Plug in your computer directly to the GX50 and enter "my.meraki.com", you'll find the settings under "Configure"
You can also change it within the Meraki Go-app. Go to Hardware -> select the GX50 -> open Settings -> you'll find IP configuration at the bottom of the list
Change the type from DHCP to Static IP. Fill in the information given to you by your ISP for IP address, Subnet Mask and Gateway and enter the Primary and Secondary DNS too. VLAN has to be left empty! Save the information and you're done.
Hope this helps.