If you bought the device used, contact the seller for the "Management Password."
Some technicians use:
Resetting an HP ZBook 15 G5 BIOS password is intentionally difficult – it’s a security feature to protect corporate data. For home users, is the safest and most reliable. Only attempt hardware methods if the laptop is out of warranty and you are comfortable with board-level repair. hp zbook 15 g5 bios password reset