How I can map the outgoing caller-id of an extension from another system

Hi all,

We have this setup below, all calls are working except the caller-id when making outgoing calls. Their existing system is not capable of setting outgoing caller-id and can only use the extension number as the caller id when passing the call to FreePBX. How I can map in FreePBX such that, when the extensions from another system make outgoing call to the ISDN line which is connected to the FreePBX it will use a specific caller-id (based on the block of numbers)- currently as it will use the mainline number for all outgoing calls. Is there any workaround for this scenario and if possible we want the modification/customization as our last option.

Setup Connectivity

Inbound Settings of FreePBX when receiving calls from the existing system.

The CallerID number is the caller-id of the extension from the other system, so if FreePBX receives a caller-id such as 200 simply route the call directly to the ISDN trunk.

Thank you!