XPS 15 9550 power fails

A problem has developed with my XPS 15 - 9550 laptop where sometimes when I press the left ctrl or otherwise press on the bottom left of the chassis there is an immediate loss of power like I had pressed the off button.  Then when I press the power button it boots up from scratch.  I ran Dell diagnostics and everythng reported fine. It is under warranty.  What is the course of action to get this resolved?