Go to the website
ams.benq.com
Once you see the screen below select login with Google. It will ask you to give BenQ permissions to access your account. Select allow.
Once you have logged in, click Personal Settings on the left hand pane. Under 'Cloud Storage' select Link next to the Google Drive option. Select which account that you want to connect, and select allow when it asks BenQ to access your Google Account.
After that you are all set. When you log into your BenQ TV, your Google Drive will show as an option in File Managment.