mobile application – Guiding users to enter their membership number from email to app

I’m designing a feature to encourage users to sign up as a frequent flyer member on a flight booking app. This feature will appear on the booking summary screen after the user has booked a flight.

This will send the user to registration. After that they will be shown a confirmation and that a confirmation email has been sent to the user.

From here there’s just 1 button that takes the user back to the booking summary. The booking summary screen all is the same except the message now welcomes the user as a frequent flyer with brief instructions on how to add their frequent flyer number to their upcoming trip to accrue the miles mentioned previously. the button here that leads them to manage booking which is a webview.

enter image description here

The challenge I’m facing is after registration the user needs to do quite a bit in order to insert their new frequent flyer number to their upcoming trip.

  1. leave the app to check their email and verify themself.
  2. get another email after being verified with their membership number
  3. copy their membership number go back to the app.
  4. in the app press the button and go to the webview
  5. in the webview scroll down and locate the part where they can enter this frequent flyer number.

My question is how can the last part of the flow be simplified for the user.

I’m facing quite a few limitations too. Here I cannot change anything on the website in the webview as it’s under a different platform.