Configure your domain name with another registrar
Step 1: Access to the DNS Zone Editor
Log in to your account on your registrar's website.
Go to the management of your domain name. Look for a section titled something similar to "DNS", "DNS Zone", "Zone File", "Manage Zone", "DNS Configuration", or "DNS Management".
Step 2: Configuring the CNAME Record
Inside the DNS zone editor, you will need to create (or modify, if it already exists) a CNAME type record.
For this record, use as Alias (or Subdomain or Name) the value www.
The Value (or Destination) of this record must be d.book.fr.
Note: Access to the option to add a CNAME record may require switching to "advanced mode" or "expert mode".
Step 3: Domain Redirection
Check if your domain name automatically redirects visitors from https://yourdomain.ext to https://www.yourdomain.ext. If this is not the case, you need to set up this redirection.
In the client interface of your registrar, look for a section titled "Redirects", "Web Redirects", or "Forward". Prefer to set up a visible and permanent redirection (301) rather than a transparent or masked redirection.
Need help?
If you are having difficulty setting up your domain name, contact your registrar. Indicate that you need to create a CNAME record for www pointing to d.book.fr, and that your address https://yourdomain.ext should be redirected to https://www.yourdomain.ext.