1. Open G Cloud App.
  2. Tap the Menu icon  in the upper left corner of the app.
  3. Open Settings.
  4. Tap the Automatic Backup option.
  5. Set Upload files to G Cloud When On schedule.

By default, G Cloud will run the backup while charging your phone and when it is connected to WiFi.

To force G Cloud to run the backup whenever you want, check this article.

This applies only for the Android version of G Cloud.