How to delete maps data after uninstalling the app on iPhone?

Reinstall the Maps app, open Maps app > tap your round account icon in the upper right > tap Offline Maps > tap whichever maps you want to delete (all of them?) > select delete.

Welcome and thank you for reaching out. 🤗

According to Apple:

1. In the Maps app, tap your picture or initials next to the search field.
2. Tap Offline Maps.
3. Tap the offline map you want to edit or delete. You can rename your map, resize the area included or view the file size.
4. When ready, tap Delete Map or Done.

NOTE: You can delete offline maps only in the Maps app.

If you need more help, contact Apple Support directly.

Good Luck! 👋🏼😉

Smiliñ 😎 Brian | Community Volunteer