missing service tag from bios Optiplex 760

A service tag is used as referencing ID to obtain service from Dell.  The machine was end-of-life and no longer obligated under warranty.  The machine can be functioning without its service tag.  That is not an issue.  There is no need of fixing it.  

chino is correct.

Re: 760 bios.  Go to bios>maintenance tab.  Does it allow you to enter a service tag there, assuming you still know the s.t. based on Dell white sticker on pc chassis.

I have a Dell XPS (old) that has a red underscore in bios where service tag ought to be. I want to know how to get rid of that. to me a blank space looks better in bios than a red _. 

Hi Chino,

The only issue we are running into is trying to do dell command updates, as it needs to service tag for this.

That's why we were hoping at some sort of fix, but it's not looking very hopeful. Have tried vio bios>maintenance tab but unable to do it there.

Dell Command Update is a stand-alone application for client systems, that provides updates for system software that is released by Dell. The application simplifies the BIOS, firmware, driver, and application update experience for Dell client hardware.

Due to age and status of system end of service life, Dell stopped releasing any drivers, software, firmware updates for OptiPlex 760 since 2015.  

Point is, missing the service tag from BIOS does not affect its performance.  Just trying to help by pointing out the reason why it is not really considered an issue whereas one would spend time and money to fix it.  However, there is paid tech service who can reprogram the service tag to the board's BIOS (using service mode), but you must search your purchase invoice and providing the original tag.

There is a maintenance task with least cost you can do, replacing the coin cell battery (CR2032) will help BIOS restore and maintain its functions. 

perhaps the command update software just needs a 760 service tag input to work, but not necessarily the s.t. associated with your motherboard.  If so, try this or look for a similar sticker on your pc chassis.