View login history in Macbook app store app
If you bought the Mac used, this could be the AppleID of the person who sold it to you. You should be able to find an option in the Store menu (Store —> Sign Out) to sign out of that AppleID. You’ll be able to sign in to your own ID after that. Be aware that apps that were provided with the Mac may need to be re-purchased or downloaded again to associate them with your ID, or to be able to use or update them after signing out.