How to turn Wi-Fi Assist on and off on my Apple iPhone 5S
When enabled, Wi-Fi Assist will allow the Apple iPhone 5S to use cellular data when Wi-Fi connectivity is poor.
Note: When Wi-Fi Assist uses data from your mobile service, charges may apply.
1. Touch Settings.
2. Touch Mobile Data.
3. Scroll to and touch Wi-Fi Assist.
4. Wi-Fi Assist is now off.
Touch Wi-Fi Assist again to turn it on.