how do i reinstall Safari on my macXO

Why do you think you have to reinstall Safari? Safari is installed as part of the Mac's operating system and as such can not be removed. The way to replace Safari or upgrade is to reinstall the OS or upgrade it.

Safari is part of macOS, and is upgraded with macOS.

Safari is part of the operating system, and is somewhat difficult to delete.

If you're on OS X 10.11 or earlier and being asked to update Safari, then your Safari is older, and you will want to upgrade to macOS 10.13 or newer if your Mac supports versions newer than what you're currently running.

How to get old versions of macOS - Apple Support

If you're unsure about any of this, please post more details about the issue you're seeking to resolve, and please use > About This Mac, and post the Mac model and Mac model year, and with both the Mac model and Mac model year, we can better provide information about available upgrade options.