You can clone single issues (Single Clone), issue hierarchies (Epic/Tree Clone) or multiple issues (Bulk Clone) from JXL.

If you have both apps installed, navigate to a JXL sheet and select the rows (or just cells of rows) of the Issues you'd like to clone, right-click in the selection to open the cell context menu, and choose Clone or Bulk Clone. A Deep Clone for Jira dialog opens pre-populated with the Issues from your JXL Sheet.

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JXL documentation about cloning issues.