If you have taken a backup of your Geneious database using the Geneious backup tool, and have a file with the suffix .backup.zip, you can restore this by opening Geneious and going to File -> Restore Backup.
Backup.zip files are entire databases by themselves and cannot be restored into an existing Geneious database. At the prompt where you are asked to choose a directory to restore the backup to, you must choose either an empty folder on your drive, or type the name of a new folder that does not currently exist (Geneious will then create the folder to restore the backup to).
After the backup is extracted, you will see the following window:
Click Load Restored Data to load your backed up data into Geneious.
Note that after you restore a backup in this way the back up data will replace any existing data you had in Geneious. However the existing data has not been deleted. For instructions on how to combine a restored backup with your existing data, please see How do I merge a restored backup with my existing data?
If you have files from Geneious in .geneious format, rather than a full database backup, you can load these into your existing Geneious database by dragging and dropping them into the Geneious window.
To load a database backed up with a system or third party backup tool, first transfer the database folder out of the backup drive and into your User directory. Then open Geneious and go to Tools->Preferences and set the data storage location to this database folder.