Spotlight indexes files on the Mac and their content to enable you to find what you are looking for easier and faster. If it cannot file the files you need, reindex it to solve problems.
The Spotlight search feature on the Mac is mostly automatic and you rarely need to do anything with it. It just works. Except when it doesn’t. It it rare, but sometimes the index becomes corrupted or files cannot be found that you know are on the disk somewhere.
Spotlight is basically just a database and the data can be deleted and rebuilt from scratch. All that is required is for the disk contents to be scanned and added to a fresh new database. Reindexing Spotlight should be done whenever searching does not provide the results you need or if the Mac’s performance is somehow suffering.
No files are deleted and the rebuilt Spotlight is better than before. It may be a good idea to rebuild it anyway once a year, just to freshen it even if there are no obvious problems. You don’t always see an error message with Spotlight and it sometimes just doesn’t show things you expect.
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Delete Spotlight index with privacy
Deleting the Spotlight index is easy, but it is not an obvious way to do it, it is done through privacy settings. Begin by opening System Preferences on the Mac.

There is a Spotlight icon, currently on the top row of icons, although Apple does sometimes move icons around in different versions of macOS. Click Spotlight to open it.

Select the privacy tab in Spotlight Preferences. Any folder or disk drive added to the Privacy tab is de-indexed and removed from Spotlight. Open Finder and then drag the Mac’s drive, called Macintosh HD on my Mac, and drop it on the System Preferences window.

An “Are you sure…” message appears warning you that searching on the Mac with Spotlight or within apps will no longer work. Click OK. That’s it. System Preferences can be closed and Spotlight data is automatically deleted because of the privacy setting.
Restart the Mac, return to System Preferences > Spotlight > Privacy and remove the disk drive. Select it and then click the minus button at the bottom to remove it. The drive is no longer private, so Spotlight will set about rebuilding the index by scanning all the files on the disk.
It can take some time if you have a lot of files and while it is working, the Mac will be a bit slower because of the effort required. Everything will be back to normal in an hour or so.
Delete Spotlight index from Terminal

There is a very simple command to delete the current Spotlight index and rebuild it. Open Terminal in the Utilities folder and type ‘man mdutil‘ to read the manual. Press Q to finish reading the manual. The command you want is ‘sudo mdutil -E /‘
Delete Spotlight index with utilities
There are several useful utilities for cleaning and optimizing the Mac and among the many functions is an option to rebuild the Spotlight index.

Maintenance is a free app for the Mac that performs many cleanup functions like deleting logs and caches. There is a Spotlight Index option that is not selected by default. Select it and run the maintenance jobs.

CleanMyMac X has many tune-up and clean-up functions. Select Maintenance in the sidebar and then tick the Reindex Spotlight option. Click the button at the bottom to perform the selected function.

Mac Cleaner Pro has speed up and clean up sections and the Reindex Spotlight function is listed in the Speed up mac section. Just tick the option and continue and Spotlight is deleted. It is automatically rebuilt.
Rebuild Spotlight index
Nothing needs to be done to rebuild the Spotlight index after deleting it. It is automatically rebuilt, providing it is not on the System Preferences > Spotlight > Privacy tab. It takes time to rebuild Spotlight and it depends on the Mac’s speed and the number of files on the disk.