Press on the home button two times, fast. The list of the apps you have been using lately will show up. Find Netflix on that list, and swipe up to close it.
Go to the App Store, and see if there is a Netflix update available. Download and install it.
Find Netflix icon on the Home screen, tap and hold your finger on it, until an X shows up. Click on it. The app will delete. The next thing you need to do is go to the App Store, find Netflix, download and install it on your iPhone.
Press and hold the sleep/wake button. Slide to turn off your device. Again, press and hold the same button and turn on your phone.
Some apps won’t work normally if the iOS is not updated. Check if a new version is available. It will fix the bug with ease.