install mac os mojave

Please see: How to reinstall macOS - Apple Support

REINSTALL macOS (SCORCHED–EARTH) 

Boot your Mac in Recovery mode by restarting and when you hear the startup chime press the Command-R (⌘R) keys until you see the Apple logo and progress bar. Use a wired USB keyboard for this.

When the macOS Utilities window appears, select Disk Utility.

Click Disk Utility > View > Show All Devices, then select the top-most drive device on the left.

Click Erase and then set the parameters: 

• Name the drive/volume Macintosh HD, 
• Use APFS format (for Catalina, Big Sur & Monterey) or Mac OS Extended (Journaled) format (for High Sierra or Mojave) and use GUID partition map scheme.  Click erase to complete the process.
• Quit DU and select Reinstall macOS.
• Follow the prompts to select the install destination drive and reinstall the OS.

How to reinstall macOS from macOS Recovery - Apple Support

How to create a bootable installer for macOS - Apple Support

That’s if you want to start over, clobbering all.