You'll find a couple of liks to recovery password generators at the bottom of this page:
https://therestartproject.org/wiki/UEFI_and_GPT
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But according to the [https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwi6z7eY5O3jAhVFsXEKHZJkCeIQFjAAegQIAhAC&url=http%3A%2F%2Ftim.id.au%2Flaptops%2Flenovo%2Fthinkpad%2520sl400%2520sl400c%2520sl500%2520sl500c.pdf&usg=AOvVaw0LSw4KccF6fAVGhjbeuySY|Service Manual] there is no procedure for resetting the Supervisor Password. You have to replace the motherboard. If you can find and replace the BIOS chip that might be a last resort solution but you’d almost certainly have to source one from another laptop of the same model, in which case you’d be better off swapping the entire motherboard.