Issue links in Jira are a helpful tool to keep track of changes throughout different issues.
In the following use case the fix version that is added to the current subtask will be copied to all sibling sub-tasks.
Add the Update linked issue or sub-task post function to the desired transition or create a new transition.
Click on Add field.
Choose Fix version/s
Choose Copy field value form current issue
Click on Add
Update the following filters according to your needs.
Check the option Update sibling sub-tasks matching the specified filter criteria.
Update linked issue or sub-task