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
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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.
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To restore your backup, choose the desired snapshot entry and click the Restore option on the right.
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The app than analyses the file
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You can now choose projects, issues, or assets (if exists) to restore.
Restore Issues
When selecting this option you will be asked to select a source project which was backed up and found in the snapshot, and a target project into which into restore issues.
A filter allows you to further identify specific issues by their summary field and the date range in which the where updated. This will help you identify chamges between the snapshot and your current state of the project.
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Select the desired issues, and click Restore.
You will see a progress indicator as the restore is being dine
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Clicking Show report, allows you to examine the results. The restored issues appear with a new Key, in order not to override any existing information.
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Restore Projects
With this option, you can restore an entire project, from the backup, as displayed for your selection.
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Select the desired project and click Restore.
Once the restore is complete, you can examine the results in the report
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Note that the project was restored into a new project, so that the original one is kept. You can now edit the issues and projects and decide what to keep.
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Restore Assets
Assets are restored for the entire site, from the backup snapshot you select.
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Again, the progress is shown and you can view the results in the report.