This free app gives you the ability to add or remove a user from a group as part of a workflow using POST functions. Select any single user picker field from an issue to determine the user to add or remove (e.g. reporter or another custom field) and specify the group in the along with the action (add or remove) in the POST function settings when configuring the workflow. You can also add an approval step so the POST function only executes following a successful approval from the appropriate team or leverage any of the other capabilities of Jira workflow.