I am sure you have all come across this issue. You are logging your FortiGates (or other devices) to the FortiAnalyzer and you experience a failure of said hardware. You have a backup of the config so you move the config over to the replacement device but now your new firewall or device is listed as an unregistered device in the FortiAnalyzer. This is actually a pretty easy issue to fix as you only have to replace the serial number of the original device with the serial of the new device. Below is the config steps to perform this via CLI of the FortiAnalyzer:

execute device replace <old serial number> <name> <new serial number>