Go to the issue view and use the "more" menu (...) to select "convert to sub-task". It will ask you what type you want to change it to, and what parent issue you want to move it under.
If you don't have that option in the menu, then your project "issue type scheme" does not have any sub-task types in it and/or "sub tasks" are disabled in global admin.
I don't use Core, but I'm sure it's the same as the other Jiras. Click on the three dots (or More in older versions) at the top right hand side and there should be a menu item Convert to sub-task. it shouldn't make a difference which state it's currently in. You would only see this menu item if you have the correct permissions.
Badges are a great way to show off community activity, whether you’re a newbie or a Champion.Learn more
Every time you release software, there's a bit of risk – that there's a bug, that something breaks, or that the feature doesn't resonate with customers. Feature flagging helps make high stakes s...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs