How to delete documents and data of an app iPhone 6s

Hi

The following support articles offer Apple's advice for managing storage space on your iPhone:

• About storage on your device and in iCloud - Apple Support
• Check the storage on your iPhone, iPad, and iPod touch - Apple Support

Documents & Data includes: Safari Offline Reading List, files stored within installed apps, and app content like contacts, calendars, messages and emails (including attachments).

To manage storage, go to: Settings > General > Storage & iCloud Usage > Manage Storage.