In order to back up your Serato library follow these steps:
In My DJ Cloud, go to the "Library Backups" menu, and make sure that Serato is selected.
Open Serato, and make a simple change, like add a file to a crate.
Close Serato.
When prompted, make sure you check the box for Serato to back up your library.
Your backup will be created by Serato, and automatically be backed up in the cloud!
After your first backup is complete, every time Serato is closed, My DJ Cloud will automatically back up your library to the cloud.
You can view and download your backups from the My DJ Cloud app at any time.