Hi,
If the Bios admin password is set, either you or the person who sold you the device has set it.
Your best option would be to contact HP support to request a .bin file that you use at startup to reset the password.
https://support.hp.com/us-en/contact-hp
If you can prove ownership you shouldn’t have any trouble getting them to send you the .bin file and instructions on how to use it.
Hope this helps