If the disk is locked with Bitlocker, then it doesn't matter if you
have the BIOS/UEFI password or not - there is no way for you to
ever decrypt the data that is encrypted with Bitlocker.
This is evidently a second-hand laptop, and the owner was very
secretive about his data.
You absolutely need to get the Bitlocker password or key from the
previous owner, as well as the BIOS password. Without both, this
computer is useless to you.
The Bitlocker password can possibly be worked around following the
post
How to format a drive encrypted with Bitlocker?
This will wipe out everything on the disk and require to reinstall
Windows from scratch. The only good news is that Windows will
activate itself automatically.
For the BIOS password, we will need the exact model of your computer,
but the chances are very low that it could be reset. You might need to
ask Lenovo Support for help, and perhaps pay for this support,
and will also need to show a proof of ownership of the computer.