Open Settings
Tap Safari
Tap Clear History and Website Data
Tap Clear History and Data to confirm
Open Settings
Tap Safari
Tap Advanced
Tap Website Data
Tap Remove All Website Data
Open Settings
Tap Apps
Tap the app you want
Tap Safari if available in the app settings
Tap Clear Cache or Clear Data if available
Open the app
Sign out if needed
Delete and reinstall the app if you want to fully clear its cache and cookies