To insert a variable angle branch fitting, go to
Ribbon: DM HVAC->Ducts-> 
Variable Angle Branch
Pulldown Menu: DM HVAC->Fittings->Variable Angle Branch
You will be prompted to specify the duct on which a variable angle branch is to be inserted.
Select duct or label to insert fitting at:
A variable angle branch fitting will be inserted on the drawing, as shown below.
