When scheduling in ShowingTime itself, you can change the Showing Agent to an agent in your office by selecting the blue button in the My Profile pane after choosing the listing. 

The Teams function in Matrix also allows you to schedule a showing for your team members.   In the “working as” view, the ‘Schedule A Showing’ link in the 360 Property View will create a showing appointment in the agent’s name that the person is working under.  This is particularly helpful when assistants or transaction coordinators are managing your calendar.