SLA data can be regenerated from either SLA for Existing Issues page or More > Regenerate SLA Data link within the issue main view.
Regenerate SLA data from "SLA Generation for Existing Issues" page
After installing Time to SLA add-on and defining SLAs, the plugin starts calculating upon issue changes. However, you may want to see SLA history for already existing issues.
Time to SLA Plugin provides an SLA data generator for already existing issues.
Under Time to SLA Plugin Menu click "SLA for Existing Issues" link.
Type JQL for issues that you want to generate SLA data.
Regenerate SLA data from "Regenerate SLA Data" link
Click More in the issue screen to expand and click Regenerate SLA Data from the list.
You can select to apply all existing SLAs
Or you can multi-select from SLAs that exist in the issue
In the dialog, click Proceed button to regenerate SLA data.