Just select the one you want to format and click on the 'Erase' tab.
Once you open the Disk Utility app, you can see all the drives on your Mac are listed on the left-hand sidebar. Open Finder and choose 'Applications > Utilities > Disk Utility' to launch the app on your Mac. If you are trying to format Mac external hard drive, you can go over the process step by step: # How to Format External Hard Drive for Mac How to Recovery Hard Drive Data on Windows.
