For this you’ll need an active WiFi and internet connection, as this procedure will download MacOS from Apple’s servers before running the installer on your Mac.
Select your WiFi network if prompted.
Select your language
Once you land on the ‘macOS utilities’ screen, select ‘reinstall macOS’, then click ‘continue’.
Follow the instructions in the installer to reinstall macOS.
Select your hard disk, then click ‘install’.
MacOS will reinstall itself. This will take a while. Once complete, follow the instructions on screen to configure your Mac.