magento-test/app/code/Magento/MysqlMq/etc/crontab.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Cron:etc/crontab.xsd">
    <group id="default">
        <job name="mysqlmq_clean_messages" instance="Magento\MysqlMq\Model\Observer" method="cleanupMessages">
            <schedule>30 6,15 * * *</schedule>
        </job>
    </group>
</config>