Export functionality is available in Jira Administration -> Add-ons section
Using this tool, you are able to make a backup of all the scheduled issues in the system along with the configuration of the add-on. It is recommended to export your Scheduled Issues before making a major version upgrade (such as from The Scheduler 4.x to The Scheduler 5.x) as an additional security measure.
To perform .xml export, log in as a Jira administrator user and click cog icon (1). After selecting "Add-ons" (2), head to "Export Scheduled Issues (3).
You can export (4) Scheduled Issues from all projects (it is set as default) at once, or export it only from selected ones. (After you click on any of existing projects, "Export type" automatically switches to "Export Scheduled Issues form selected projects only".)
Additionally, you can skip exporting inactive (5) or invalid (6) Scheduled Issues.
After clicking on "Export" (8) button at the bottom of the page, The Scheduler will generate an .xml file for you to download, with a name (7) as set automatically, or modified by an exporting user.