To add a resource record (like a CNAME or A record) to your domain name's zone file, you need to follow these steps.
Go to your domain's management page and look down to the “Zone files” area that is on the bottom right-hand side of the page.
Now, at the bottom of the page under “Zone files” you will see a link to “Edit the zone”. Click the link:
If the copy you just made of the original zone file was a “public” zone (i.e. Gandi default), it will already been activated. You cannot edit an active zone file, so you must click “Create a new version.”
Tips on the syntax of each resource record type can be found on the following pages:
Once you are done making your changes, click “Use this version”:
You will be prompted to confirm:
And should then receive confirmation:
Note that changes to your zone file will take from several minutes to several hours to propagate!