The backup restore is done through the existing Jira clout Import mechanisms, as described here. Once you decided on the backup file to be imported, follow those Atlassian instructions carefully.
NOTE THAT A RESTORE IS GOING TO OVERWRITE YOUR EXISTING SITE DATA. MAKE SURE YOU UNDERSTAND AND FOLLOW THE INSTRUCTION CAREFULLY.
A good practice before an import attempt it to backup your Jira cloud site information before the import. It is also best to import the information to a secondary cloud instance. Importing to this “staging” site first will help you ensure that the restore is working well, as well as verify that the data you imported includes what you expected.
When you restore a Basic Backup, you will need to click Import Data and select the file from your local storage.
The file will then upload into Jira (you should see a progress bar) and will get processed. If everything is correct you should be redirected to a new page, with a confirmation
We've checked your file for issues, and everything looks good.
A click on Run Import will open a Running Import screen. You should then see an import progress status step after step
When done, you should get an Import complete confirmation
Your data file was successfully imported to Jira Cloud.
Follow Atlassian's verification instructions in that page, to ensure the health of your updated site.
Add extended backup