Open the "SIP Trunks" tab
Add a new SIP trunk
Under the General tab add your Main Trunk No as +1 (your DID) ex. +17019299797
If you have more DIDs, click on the "DIDs" tab at the top and add other DIDs in the same format.
Click "OK" at the top to save changes
Any Outbound Caller IDs you set will need to have the +1.
You can follow our guide for setting up outbound rules so you do not need to dial +1 when calling out of the system.
You could also read our written tutorial here.