Here's a video on How to Use the Call Forwarding feature and how to set it up. Below the video are the written set up instructions.
*Call Forwarding is only available on the Full VOIP dialer plans.
Go to Settings> Phone Dialer & Call Queues> Phone Numbers
Click on the Options button next to the phone number you want to set forwarding for
Set the number to forward to. Click Save Information.
4) Now in your Dialer, you'll see the option to start forwarding calls. Click on that option. To stop forwarding calls, go back to your Dialer which now says Forwarding Calls and choose Stop Forwarding Calls.