magento-test/app/code/Magento/Customer/Test/Mftf/ActionGroup/SetGroupCustomerActionGroup.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
 /**
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
-->

<actionGroups xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
              xsi:noNamespaceSchemaLocation="urn:magento:mftf:Test/etc/actionGroupSchema.xsd">
    <actionGroup name="SetCustomerGroupForSelectedCustomersViaGrid">
        <annotations>
            <description>Clicks on the 'Actions' dropdown menu. Clicks on 'Assign a Customer Group'. Clicks on 'Ok'.</description>
        </annotations>
        <arguments>
            <argument name="groupName" type="string"/>
        </arguments>
        
        <click selector="{{CustomersPageSection.actions}}" stepKey="clickActions"/>
        <click selector="{{CustomersPageSection.actionItem('Assign a Customer Group')}}" stepKey="clickAssignAction"/>
        <executeJS function="document.getElementsByClassName('action-menu _active')[0].scrollBy(0, 10000)" stepKey="scrollToGroup"/>
        <click selector="{{CustomersPageSection.assignGroup(groupName)}}" stepKey="selectGroup"/>
        <waitForPageLoad stepKey="waitAfterSelectingGroup"/>
        <click selector="{{AdminConfirmationModalSection.ok}}" stepKey="acceptModal"/>
    </actionGroup>
</actionGroups>