Edit your zone file in '/var/named' directory.
For example, for a "example.com" domain, the file '/var;named/domain.com.db'.
And add the following at the final of that file, for exemple to the Let’s Encrypt certificate authority,:
example.com. CAA 0 issue "letsencrypt.org"
If you want to allow Let’s Encrypt for wildcard certificates, then you can use issuewild:
example.com. CAA 0 issuewild "letsencrypt.org"
Save the changes, and restart named:
(for CentOS 7)
# systemctl restart named
(for CentOS 6.*)
# service named restart