Unfortunately when you remove an app from an iOS device, all data stored with that app is deleted.

If the device was backed up before the app was removed, then restoring that backup should restore all of the files automatically. How that's done depends on how the backup was done so I'd suggest looking at Apple's help documentation for assistance in doing the restore.

If the files were manually shifted to an external location (eg. exported to the Files app's iCloud Drive folder) then they can be manually re-imported from the menu in the gallery.

Hope that helps!