create a subdomain cloudflare. code example

Example: add subdomain on cloudflare

To create a subdomain, in the DNS tab, you add a record with the name of the 
subdomain, pointing to your host. They will specify whether it needs to be an
A record or CNAME etc. And give you the content of the record.

reference:
https://community.cloudflare.com/t/adding-subdomain-to-cloudflare/57647