To move all the requesters and technicians to the new domain without creating new login accounts for the existing users,

1. Go to Admin -> Windows Domain Scan.
2. Edit and rename the old Domain name to the new one and enter the credentials of the new Domain.
   This will change the Domain information for all the user accounts which were associated with the old Domain to the new Domain.
3. Next, go to Admin -> Requesters -> click Import from Active Directory option.  [  Screenshot ]
4. Click Import Now  [  Screenshot ]
5. Click Fetch OUs from Active Directory Again to start importing.  [  Screenshot ]