Here are some recent builds of iTunes direct from Apple's secure servers in case you want to try reinstalling the current build or try working with an older version when the current build doesn't work properly for you for some reason:
Note: macOS Mojave includes iTunes 126.96.36.199 at launch. There is no standalone installer provided.
|(2018-07-09) Current build for download|
|(2018-09-12) Last build to support app management in iTunes|
iTunes isn't particularly easy to remove from OS X but it should be possible to install the 188.8.131.52, 184.108.40.206, or 220.127.116.11 builds over any later version, and then install the build you require as long as it has a higher build number. See Deploy apps in a business environment with iTunes - Apple Support for more on these builds. Note these builds are not compatible with macOS Mojave.
If you want to install an even older build then you can try this approach to remove iTunes:
Open Finder > Applications > Utilities > Terminal
In Terminal type cd /Applications/ and press enter to open the Applications directory
Type sudo rm -rf iTunes.app/ and press enter to delete iTunes
You will be prompted to provide your administrator password which you should enter to complete the process
You may need to temporarily disable system integrity protection (SIP) while you are removing iTunes.
Rolling back your library
When reverting to an earlier build of iTunes you may need to restore an older version of your library database using, for example, the method shown in Empty/corrupt iTunes library after upgrade/crash or from another suitable backup such as Time Machine. Until you do so iTunes may tell that your library needs a newer version of iTunes. Reverting to an older version of your database will mean that you lose recent changes to your library, however you can add the media folder to the library to import recent additions.
Related support articles