In your Android Settings, disable NFC (found in "More" under Wireless & Networks). This will prevent the Daydream enviroment from launching when you put your device in the headset.
Visit RealJamVR.com in your mobile browser (Google Chrome) and login to your RealJamVR account. Select and download the 2880x1440 format you would like to see. Videos are saved in your download folder by default.
The DEO VR main menu includes your file management and video player options. Select the file folder in the main navigation to explore your Smartphone and open the previously downloaded VR video.