Suppose your example.com knowledge base URL is https://example.myfaqprime.com and you want it to be known as http://help.example.com (unsecure). Just visit your DNS record i.e. your domain providers such as godaddy.com or name.com or something similar and create a CNAME record pointing to example.myfaqprime.com here is full instruction set -
Login to your Domain Control Panel
Go to the section which says DNS or Name Servers
Create a new CNAME record with name/host/alias as your custom support URL pointing to value <example>.myfaqprime.com
TTL: Enter a Time To Live between 30 minutes to 1 hour, or leave this field in its default settings
Save changes to your DNS records.