Once you've logged in with one Google Drive account, you cannot simultaneously add a second in Studio. You may however, logout of one Google Drive account in order to login to another.

For information on how to link a google drive account via the vApps page, refer to TouchCast Studio: Google Drive vApp

1. On the opening page tap on your your channel which lives on the lower right corner. 

2. Tap settings on the top right corner of your channel page.

3. Tap "Google Drive" on the bottom of the page above "Delete Account"

4. Tap "Unlink Google Drive". Now you can return to the vApps page and link a new Google Drive account.