The Is current user in custom field validator allows you to block a workflow transition if the user executing the transition is not set in the selected custom field.
Select a custom field in the User Picker custom field field to validate the user executing the transition against being set in this field
Define the text of the error message in the Error message text field (e.g. “You are not set in the Business Owner field”)
Activate the JQL condition option and define the JQL query that has to be met by the issue in order for the validation to work (e.g. “type = Bug and Priority = Blocker”)
Activate the Executor condition option if you want the validator to work only if the user is or isn’t in a certain Jira user group or project role
Select if The executor has to be or can’t be a member of a certain Jira user group or project role
Select a Jira user group in the Group field if Group was set in the member of a field
Select a project role in the Project role field if Project role was set in the member of a field