You should always take regular backups of your data files. Due to the way the local database works, it is important that Geneious is not accessing the database when a backup is taken. The safest way to make a backup is to use the backup function in Geneious, under File -> Back Up Data. This will cause Geneious to cease working on the local database and make a zip archive of the entire database, including all preferences and settings. This file should be stored on another drive.
You will need to ensure that the drive you are making the backup to contains sufficient space for your data before you start the backup, otherwise it will fail. The backup will take approximately the same amount of space as your existing Geneious data folder.