First run this
mysql -B -u zabbix -pxxx zabbix -e 'SELECT CONCAT("ALTER TABLE ", TABLE_NAME," CONVERT TO CHARACTER SET utf8 COLLATE utf8_bin;") AS ExecuteTheString
FROM information_schema.`COLUMNS`
WHERE table_schema = "zabbix" AND COLLATION_NAME = "utf8_general_ci";'
After that paste command output to another
mysql -B -u zabbix -pxxx zabbix -e '<paste here>'