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On the top right section of the Relations page, you will find the button “Migrate Links”, which will allows allow you to convert regular issue links to advanced issue relations, and vice versa:
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By clicking on “Migrate Links”, a pop up screen will appear asking you to select by JQL the issues within which you want to migrate the links and to map the source link with the corresponding relations:
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In the Relation tab of the same screen, you can migrate advanced issue relations to native Jira links:
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