The Atomic platform will pass through the CLI that your end device passes to the platform. In the case where if you are using a SIP End Point to call out, and if you do not set your User Agent's CLI, the call will display your Account Number by default. This number generally starts with a "9990xxxxxxxxxx".
The configuration for your CLI should be done on the User Agent level. To find out more on how to configure this, you will need to refer to your device manual provided to you by the manufacturer.
However, you can use the Atomic portal to help set up the CLI number for you. In the Account Settings > Advanced Settings, under the 'CLI Translation' label, select the DID number that you want sent when placing a call from the Service.
Default option is selected, the Atomic switch will only use the CLI that is passed on by your switch/device. Do remember that this would mean that all calls from that Service will display the same CLI number. If you have multiple users or User Agents connected to the same SIP End Point, all calls made will have the same CLI appearing.
The only way to have different CLI's appearing for each user or User Agent, is to setup the CLI configuration on the User Agent's device.