Copy values

[Cristina - Elena Andrei]

Hi. I would like to copy the assignee value from a parent issue to a substask. Also i would like to copy a value from a insight field from a parent to a substask.  Assignee and insight field from parent - standard isssue to copy to the child issue. 

To do that i would like to use postfunctions and conditions. I would mention that the environment is data center. I don't have scriptrunner. Only automation rules or workflow toolbox.

Also the parent issues are already created and also the subtask. I need to copy the assignee and insight field from parent to substask.

Elements Copy and Sync is working only when I create new subtask.  What i want is to update the existing ones.

How i can do this task? Any idea or suggestion will help me a lot.

Thank you!