[help] modify the outgoing message sent by voice gateway to PSTN to be valid in

Lion

The company‘s branch office in a certain city uses IP phones. When calling outside lines, the number of the switchboard is displayed. The service provider says that the telephone number information sent to them by our voice gateway is "unknown" and needs to be modified to "valid in China"... How to modify this? The voice gateway is Cisco 2951.. thank you!