Hi Mustafa,
Updating domains for an Enforce-managed Cloud Detector is done in the Enforce console.
Update Email Domains in the Enforce Server Administration Console
If you have the Cloud-Managed Detector, it is done in the CASB / CloudSOC UI:
Adding and validating SMTP domains
Adding domains requires them to have a TXT record, the steps for which are outlined in the linked pages above.
Hope this helps.
Cheers,
Stephen