Adding CNAME record for a domain with subdomain
In this case your custom domain will look like
calendar.yourbusiness.com
Log in to your AWS Route56 dashboard
Go to Hosted Zones and select your domain
Click on Create record
Select CNAME as the Record Type
Add Record Name and Value
Select 1m for TTL
Keep the Routing policy as Simple Routing
Click on Create Records
For more information refer official documentation
Adding CNAME record for a root domain
We cannot set a CNAME record for the root domain in AWS Route 53