Need to reset BIOS administrator password on Precision 7710 laptop

One of our colleagues recently passed away. In going through his work area, we located a Dell Precision 7710 laptop that was being used to administer several systems.  We need to access the BIOS and make a couple of changes in order to repurpose the device. However, it has an Adminstrator password on it that is preventing us from doing so. We cannot locate the bill of sale or a receipt of any kind.  This is an IT shop supporting the Naval Sea Systems Command in Washington, DC.  We have tried using the method of removing the battery, disconnecting the button cell battery, and removing power, and then holding down the power button for as long as 2 minutes, but the BIOS password has not reverted back or cleared. Is there any other way we can get this BIOS password reset?  I know there is a process by which we can provide the service ID for the machine and Dell Support can give us a code to clear it, but as I said, we cannot locate the bill of sale or any invoices or receipts for this device.  The ID that shows on the screen where the password gets entered is 8R90L72-E7A8. Any help that can be provided would be greatly appreciated.