Login to your 123 reg account, select the domain you want to point to your site on Fixers and select manage domain.
Once here select manage DNS and Advanced DNS settings.
Scroll to the bottom of the page and you'll see empty fields ready for you to configure your domain.
Enter www as your host name
Select type CNAME
Enter ssl.fixersworld.com as the destination
Now press add and you should see your new configuration added to the list of records. Your domain should now be set up on www.yourdomain.com
Next you need to set up a redirect to ensure your domain loads without the www. prefix e.g yourdomain.com follow these extra steps.
Under domain basics select Web Forwarding.
From here select your domain and select a permanent redirect. When prompted enter www.yourdomain.com to configure the redirect.
Your domain should now be good to go on www.yourdomain.com.