How can I use WebDav on my iOS device?

You can use WebDav on your iOS device by connecting a server using the Files app.

Please follow the instructions provided by Apple at the following link: 

https://support.apple.com/en-gb/guide/iphone/iph8d8f0f1a0/15.0/ios/15.0.

Once connected, you can import files from WebDav into the Notes Writer app. To do this, simply open Notes Writer, tap the home button on the bottom tool bar, and select "In Files app". This will take you to the Files app, where you can access and import your WebDav files.