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I have an epic that has child issues and sub-task. Need to move all the sub-tasks as a child issue. All the issues should appear as a child issue and the issue type should be a story. The project is in a company-managed setting.
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You will need to go into each sub-task and use the "change to issue" function in the options menu. It will ask you what issue type to change to.
After that, you'll be able to edit them and set the Epic-link.
Go into the epic and above the sub-tasks click on the three-dot menu -> Bulk Edit.
You can then change the issue type of those sub-tasks to be story, task, etc. en masse.
Before doing that, I'd keep a separate tab open with the same epic loaded, so you can refer back to it and see which tickets you now need to assign back into the epic, as I'm not sure they'll retain their epic when you change them to be non-sub-tasks. You can bulk edit to assign them to the epic too.