When ooVoo is installed on PC and you Add Friends one of the options is linking to your Gmail account, and you will see this screen:
If you allow, then it will link to your Gmail account. To remove these permissions
Log into your Gmail and go to My Account:
Click on My Account. Under Sign-in & Security go to Connected apps & sites.
Select ooVoo and then select remove:
This will un-link your Gmail from ooVoo.