1. Go to PBX Monitor → Trunk to check the status of the trunk and make sure the trunk is available to use.
2. Go to Settings → PBX → Call Control → Outbound Routes, click in the outbound routes list page.
3. Fill in the details in the edit page and save. For example, you could configure the outbound routes as follows if you want 1000, 1005 and 1006 to use FXO1-7 to dial out.
For more details, please refer to the S-Series VoIP PBX Administrator Guide.