How can I restore iTunes

The iTunes app for Mac computers was discontinued and replaced when macOS Catalina was released. It cannot be installed on Macs that are running Catalina or later. See the following Apple article for information about the replacement apps: What happened to iTunes? - Apple Support

Apple split iTunes up in Catalina; use the new applications instead. Click here for more information.

If you're referring to music instead of the application, restore it from a backup or reload it from the original source.

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