Try force closing the app - double tap the home button so that you see the App Switcher, then slide the thumbnail towards the top of the screen.
If that doesn’t help, restart your iPhone.
If the information in your signature is correct, you’re still running iOS 10.3.3 on your iPhone 6. Updating the iPhone would be the next step, if the two measurements above don’t help. The latest software for the iPhone 6 is iOS 11.3.
Try force closing the app - double tap the home button so that you see the App Switcher, then slide the thumbnail towards the top of the screen.
If that doesn’t help, restart your iPhone.
If the information in your signature is correct, you’re still running iOS 10.3.3 on your iPhone 6. Updating the iPhone would be the next step, if the two measurements above don’t help. The latest software for the iPhone 6 is iOS 11.3.