cd /var/named
replace 'ns1.olddomain.com' 'ns1.newdomain.com' -- *.db
replace 'ns2.olddomain.com' 'ns2.newdomain.com' -- *.db
You have to replace ns1/ns2.olddomain.com and ns1/ns2.newdomain.com with the correct nameservers.
Restart named using the command
service named restart
named -u named
ls /scripts/ | grep named
/scripts/rebuilddnsconfig
Also remember to change your nameserver too
vi /etc/nameserverips