From the manual:
ftp://ftp.hp.com/pub/networking/software/59906023-1004-Management-Guide.pdfIf You Lose a Password
If you lose the passwords, you can clear them by pressing the Clear button on
the front of the switch. This action deletes all password and user name
protection from all of the switchâ s interfaces.
The Clear button is provided for your convenience, but its presence means
that if you are concerned with the security of the switch configuration and
operation, you should make sure the switch is installed in a secure location,
such as a locked wiring closet.(For more information, refer to â Front Panel
Securityâ in the chapter titled â Configuring Username and Password Securityâ
in the Access Security Guide for your switch.)