The clip gain envelope
Can be moved without moving the clip.
With track edit filter set to "Clip Automation-Gain", select the clip. That will select all of the envelope nodes in the clip. Hold down the Cntrl key and click on the nodes at each end of the clip to un-select them. Then while still holding down the Cntrl key, you can move the envelope forward or backward
to the boundary of the clip. Note that if there are nodes at the boundary, they will move no farther.