You would need to work with your VPN provider. Is this a personal VPN or company? If company, you should explain the problem and ask if the VPN is setup as 'split tunnel' this is where the VPN is used to access company resources, but general internet traffic routes normally.
Using a split tunnel would defeat the purpose of using a VPN connection in the first place. If you want to have your communications protected then you want the VoIP to pass through the VPN not around it. Is there a way to have RingCentral work through a VPN connection?