Unable to use KoBoToolbox in iPhone

We have followed the instructions as per KoBoToolbox manual for enabling KoBoToolbox for iPhone (link attached below), we are still unable to revert to Enketo Webforms in iOS.
Need your answers on how to conduct data collection in iPhone.

Collecting Data through Web Forms — KoBoToolbox documentation

Which browser does your device (iPhone) use? Could you also check out if your device has some modern browsers that compatible with your device as outlined in our support article Troubleshooting Enketo Web Forms?