The Reset Label to Default Location command is used to undo any changes to duct labels moved by the Move Label command, rotated by the Rotate Label to Angle 0 command, or removed by the Remove Label command.
To reset a duct label to the default location, go to
Ribbon: DM HVAC->Ducts-> 
Reset Label to Default Location
Pulldown Menu: DM HVAC->2D Drafting->Reset Label to Default Location
You will be prompted to identify the duct label to be reset.
Select duct or label to reset:
The label will be reset to its original location and orientation.