Kindly follow below steps to preview Oculus Go app.
1. Open the your project.
2. Navigate to "Preview" section.
3. Click on "Download" button which is beside Oculus GO/GearVR platform.
4. Once, download is completed, side-load the downloaded app to Oculus Go using ADB method.
5. Open the Previewer app from the "Unknown Sources" under "Libraries" section in Oculus Go.
6. Use the InstaVR credentials (username and password) to view the list of projects and open the app that you would like to preview.