On FortiGate 6.4 and higher, you should find FortiManager under Security Fabric > Fabric connectors, and can edit the entry to point the devices to a local FortiManager.
It would probably be a bit easier to just discover the devices from FortiManager though.
You would have to do the following:
- ensure the interface on FortiGate that FortiManager should communicate with has FMG-Access enabled
- log into FortiManager
-> if you haven't already, enable ADOMs and create several to reflect the various FortiGate firmware versions (do note that 5.6 might not be supported by a FortiManager that supports 7.0)
- go into the appropriate ADOM for the firmware version, to Device Manager and click on 'Add Device', then go through the steps
-> FortiManager will connect to FortiGate and start managing it.
+++ Divide by Cucumber Error. Please Reinstall Universe and Reboot +++