how do I use disk utility on macOS Base System

Dr. Sheila wrote:

I am trying to wipe out my old macbook pro but when I go to the Disk Utility, instead of Macintosh HD I just find macOS Base System

Sounds like you did wipe out your macOS...

Base System is the Recovery Volume— what is your bigger issue here?

Boot into Internet Recovery (Option Command R) and from the dropdown menu: Utilities>  Disk Utility> run the First Aid on your Macintosh HD (and the "Macintosh HD-Data" volume as well if Catalina/Big Sur) If errors are found and repaired, run again until no errors reported.

Disk Utility>View>Show All Devices The best sequence is —

• Volume level

• Container level

• Parent drive

Recovery: https://support.apple.com/en-us/HT204904

How to reinstall macOS from macOS Recovery - https://support.apple.com/en-us/HT204904

'MacOS Base System' is a name used for the ROM-resident Recovery software AND can be used as the name of the incoming Installer software.

Neither will benefit from being repaired.

If their is no additional device showing, even after you have selected 'View All devices', you have a much larger issue than just a simple repair -- your boot drive has died.

¿what model-year MacBook Pro?