This technique of resetting your MacBook Air to its factory state should only be applied in a persistent Bing redirect scenario where all the other fixes end up futile. Be advised, though, that you need to back up all your personal data first otherwise you’ll lose it for good. Thankfully, macOS is equipped with the Time Machine utility that allows you to back up all the files to an external storage device without using any third-party apps. The procedure is as follows: Plug the backup disk into your Mac Open Time Machine and click Select Backup Disk Pick the external drive you’d like to back up your MacBook Air to Enable the Encrypt backups option for extra security, click Use Disk, and wait for the backup to be completed. To perform the reset proper, boot up your MacBook Air in Recovery Mode. This is doable by long-pressing Command + R keys when your computer is starting up or restarting. Release the buttons once you see the Apple logo and wait for the macOS Utilities window to appear. Here’s what you need to do next: Select Disk Utility in the macOS Utilities screen and click Continue Go to View and select Show All Devices Choose your hard disk and click Erase If you are using macOS High Sierra or later, select APFS in the Format area. Otherwise, select Mac OS Extended (Journaled) file system Click Erase again. Now that your hard disk has been wiped, you need to reinstall the operating system. Follow these steps to do it: In the macOS Utilities screen, select Reinstall macOS Click Continue Follow subsequent prompts to complete the reinstall. Once you start fresh with your MacBook Air, you can import your data from the backup disk and customize the system along with the software you use.