Restoring iPhone from a backup located on an external hard drive

Hello, I recently had the infinite reboot problem on my iPhone 11 and was forced to restore it and lose all my data. I have a backup of this iphone stored on an external hard drive but when I press Restore Backup, no backup can be located. It also says that the last backup on this mac is unknown. How will I be able to restore my iPhone from the backup located on my external hard drive? Thanks.