You need to make a gateway network connection to your other gateway (Configure -> Connections -> Gateway Network) - that’s where you will enter the remote gateway’s IP. Once you’ve done that, you’ll enter that gateway’s name (not it’s IP address) in the Remote Gateway Name field.
You will likely also need to configure ‘Service Security’ on the remote gateway to allow the edge gateway to store history using its history provider.
https://docs.inductiveautomation.com/display/DOC80/Gateway+Network#GatewayNetwork-SettingUpaGatewayNetworkConnection
https://docs.inductiveautomation.com/display/DOC80/Security+Zones#SecurityZones-ServiceSecurity
https://docs.inductiveautomation.com/display/DOC80/Edge+Sync+Services#EdgeSyncServices-DataSynchronization