If you've forgotten the UEFI/BIOS password on a Microsoft Surface Pro 3, there is unfortunately no user-accessible reset method.
UEFI passwords are used primarily by enterprises and IT professionals to limit the types of changes that employees can make to their devices. If you're part of an enterprise, contact your IT administrator if you have any questions or issues with your UEFI password. If you aren't part of an enterprise and choose to create a UEFI password, make sure to document your password in a safe place. You can't reset your UEFI password, and Microsoft can't retrieve it.
Ref: