What version/edition of TC?
From V12 through V16 the "Flip" commands will become available in the Local Menu and Inspector Bar when you select a Door/Window with the "Edit Tool", not the "Select" tool. In Version 16 they added the flip feature to the Local Menu and Inspector Bar when inserting a Door/Window.
Designer, Deluxe, (Professional, Expert, Basic), Platinum
Windows 10 Pro (1803), 64-bit