Retrieve configuration even if you forget password?

If you forget the password and don't have any other active password for the device, login is not possible and can't download the configuration backup. If the device is managed by FortiManager, you can get the configuration from Fortimanager.

If you forget the IP, please check any connected swicth/PC for ARP table or GW, there are very high chances the firewall is GW and you can get the IP.

Have you tried to password reset using "maintainer" username?

Or, you can try FortiOS boot option during OS loading time by pressing "spacebar" key. There might be an option to retrieve old config and backup/alternate OS to boot.

Maintainer account will be working till 7.2.3 

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Resetting-a-lost-admin-password/ta-p/197045

To add on, On some devices, after the device boots, only an entry window of 14 seconds or less is available to type in the username and password.

Verender