Thank you. I have deleted the MySQL file and upgraded Mysql to 5.6 in custombuildI would not revert if I were you, but if you do, take care for decent backups.
Mysql is normally present in /var/lib/mysql
System backup of mysql (on upgrade for example) will be in /usr/local/directadmin/custombuild/mysql_backups
And php normally in /usr/local/phpXX where xx is the php version.
How to uninstall mysql5.7 and install mysql5.6 in DirectAdmin ,