If standard options are unavailable, third-party solutions exist but carry significant technical risks:
Understanding HP EliteBook 840 G6 BIOS Password Reset Utilities
Do not fall for scams promising "instant download software" that claims to reset the password from within a locked screen—that is impossible. The real utility either requires a second computer, a hardware programmer, or a support call to HP.
(official channel)
6.2. EEPROM/BIOS chip reprogramming or replacement
