In this case, your custom domain will look like
https://form.yourbusiness.com
Log in to your DigitalOcean dashboard.
Go to Networkings -> Domains.
Select your domain from the list.
Click on the CNAME section.
Fill the HOSTNAME, IS AN ALIAS OF and TTL fields as seen on the custom domain setting page on NeetoForm.
Click on the Create Record button.
For more information, refer to the official documentation.