Add a default message to my app, if no sms messages are found (Android Studio / Kotlin)

My app checks user phone of sms messages.
App checks which of the messages are 1 month old and newer.
App checks which of those messages contain an URL.
App shows user the list of such messages.

At the moment if no such messages are found, app whill show a white screen.

Project: If no messages are found, add popup "no messages found"-text and button to exit the app.
I will provide the actual text for the popup.