The Custom Domain feature is avaliable for 
paid plans only.
- Add your custom domain in account settings
- Go to your DNS provider and set up a CNAME record for your subdomain that points to the value shown on the account settings page
- Wait a few minutes for the SSL certificate to be generated
 Screenshot from 2021-04-21 12-15-45.png 41.55 KB
Screenshot from 2021-04-21 12-15-45.png 41.55 KB
Make sure to consult with your DNS provider for specific instructions to create CNAME records.