I would take a look at the Communities post When you create a sub-task can you automatically inherit certain fields from the parent for the way others have resolved this issue in their instances:
Here is the advice from one user:
"In the create issue transition you can set the "Set Field Value from Parent" option in the post-functions. You can either do this in the default workflow you are using for the project, or make a separate workflow for sub-tasks. When only using this post-function, changing the value of the field in either the parent or sub-task will have no influence of the others value."
In addition you can also try Automation for JIRA.
Hi Atlassian community, My name is Max and I work on the product integration team at Atlassian. I am pleased to announce the early access program for the Jira Cloud add-in for Outlook. This add-in...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events