Dell does not provide a public-facing "unlock tool" for consumers. However, large enterprises with Dell ProSupport contracts can call Dell with proof of ownership. Dell will generate a based on the Key Hint Number over the phone. This password is typically between 32 and 34 characters long.
Store BIOS passwords in a secure password manager. Dell Bios Password Unlock Key Hint Number
You provide the Service Tag and the Key Hint Number. The agent provides a one-time master password. Dell does not provide a public-facing "unlock tool"
For older Dell systems, removing the coin-cell battery (CMOS) for several minutes can reset BIOS settings to factory defaults. Dell Bios Password Unlock Key Hint Number