The TomTom Navigation app for iPhone is no longer available for purchase.

Rapid changes in TomTom and Apple technologies mean that we cannot continue offering updates to this app indefinitely. For this reason, we will not be supporting this app from September 2017 onwards. More information will follow in our next update.
Until this time, you will receive map and software updates and we hope that you will continue to enjoy using the iPhone Navigation app.

If your app is still installed on your iPhone you are alerted in the Updates tab of the App Store app whenever an update is available.

If your app is not installed on your iPhone you can follow Apple’s steps for redownloading past purchases available through this link:
Redownload apps, music, movies, TV shows, and books from the iTunes Store, iBooks Store, and App Store