You can easily export existing test cases to a CSV file. You can select to export all of the test cases that are available on your Jira instance or you can select the data you want to export using a JQL or applying a Jira filter.
This is a feature available only with QAlity Plus.
To export your test cases go to Advanced issue search. Based on the filter or JQL search determine which test cases you want to export. Then click on the QAlity (QAlity bulk button on Jira Server) and select Export Test Cases option. Save your file and