If your domain is registered on 123-reg, you should follow this tutorial to update the nameserver of your domain to our nameserver.
1. Open the 123-reg.co.uk website and click on "Control Panel". It will show you a login form.
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2. Enter the username and password of your 123-reg account and then click the "login" button.
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3. After a successful login, select the appropriate domain from the dropdown list and then click on the "Manage" button.
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4. Scroll down to the "Advanced domain settings" and then click on "Change Nameservers (DNS)".
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5. Enter your Nameserver in field 1 and field 2 and then click on the "Update" Button.
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You will see a success message.
Note: It may take anywhere from 12 to 24 hours for the changes to take effect worldwide.