To create a new CNAME record, follow the subsequent steps:
Click on Nameserver in the left side menu.
Click the eye symbol button () of the respective domain to show it's DNS Entries. If a CNAME record already exists, you can modify it.
Click on Add DNS entry.
Enter the CNAME:
Under the column Name you can enter a subdomain for the CNAME e.g. www.
For Type Choose CNAME.
Enter the CNAME address into the field Value.
To conclude the modifications click on Save.