The app version will start with a build 0.0.0 and progress incrementally. So 0.0.1, 0.0.2 etc etc.
When you generate a Commercial build to submit your app to iTunes or Google play you'll need to bump the version number up to at least 1.0. Additional builds will progress 1.0.1, 1.0.2 etc.
To change the version number of the app first click on the three dots next to your app name, then click "Configure"
Go to the "General" tab.
Scroll to where it says current version. Here you can change the app version to any version number you wish. NOTE: You can't reverse this number. You can only bump up the app version number.