As your host for the path to the "mysqldump" binary.
And then set that path in the language file:
/admin/includes/languages/english/backup_mysql.php
Code:
// define the locations of the mysql utilities. Typical location is in '/usr/bin/' ... but not on Windows servers.
// try 'c:/mysql/bin/mysql.exe' and 'c:/mysql/bin/mysqldump.exe' on Windows hosts ... change drive letter and path as needed
define('LOCAL_EXE_MYSQL', '/usr/bin/mysql'); // used for restores
define('LOCAL_EXE_MYSQLDUMP', '/usr/bin/mysqldump'); // used for backups
Similar instructions are in the readme for this contribution.