Hi @Apoorva,
From the link Mike posted, states
“Since Let’s Encrypt follows the DNS standards when looking up TXT records for DNS-01 validation, you can use CNAME records or NS records to delegate answering the challenge to other DNS zones. This can be used to delegate the _acme-challenge subdomain to a validation-specific server or zone. It can also be used if your DNS provider is slow to update, and you want to delegate to a quicker-updating server.“
Also see: CNAME record - Wikipedia
Edit
And here is on suggest example DNS-01 challenge acme-dns internal Bind - #12 by jvanasco