Android Studio Run/Debug configuration error: Module not specified

Resync your project gradle files to add the `app` module through Gradle

In the root folder of your project, open the settings.gradle file for editing.
Cut line include ':app' from the file.
On Android Studio, click on the File Menu, and select Sync Project with Gradle files.
After synchronisation, paste back line include ':app' to the settings.gradle file.
Re-run Sync Project with Gradle files again.

never mind, i changed the name in settings.gradle and synced and then changed it back and synced again and it inexplicably worked this time.

android android-studio module gradle

Try to delete the app.iml in your project directory and restart android studio