In CSM Workspace how to add new ui action over compose email record

[kuldeep9]

I am able to create ui action on service case table within workspace because that is a direct record not a sub record or related table navigation but when i need to create a ui action for adrill down view or a supporting table-- in my case from service case record I go to compose email>> which is a sys_email_draft table subrecord that gets opened, here I need to add a new ui action. please see screenshots added. Anybody who has done ui action over compose email record?