MS Access is not a RingCentral product so we are by no means experts on it. If you know how to shell a command line with MS Access, here is the command line command for you: 'open rcmobile://call?number=xxxxxxxxxx'. This command is for macOS. For Windows you might need to adjust it.
You can program Access to do everything through the API. I have some subroutines that can save you time like getting the Access Token, encoding in base64, sending an SMS message and retrieving the responses which I'd be happy to share.