This file will modify the rowaction buttons on subpanels and add a delete button. The delete functionality must include subpanel-list.js file.

subpanel-list.php

<?php
if(!defined('sugarEntry') || !sugarEntry) die('Not A Valid Entry Point');

$module = "YOUR_MODULE";
$viewdefs[$module]['base']['view']['subpanel-list'] = array(
    'template' => 'recordlist',
    'favorite' => true,
    'rowactions' => array(
        'actions' => array(
            array(
                'type' => 'rowaction',
                'name' => 'edit_button',
                'icon' => 'icon-pencil',
                'label' => 'LBL_EDIT_BUTTON',
                'event' => 'list:editrow:fire',
                'acl_action' => 'edit',
                'allow_bwc' => true,
            ),
            array(
                'type' => 'rowaction',
                'css_class' => 'btn',
                'event' => 'list:preview:fire',
                'icon' => 'icon-eye-open',
                'label' => ' Preview',
                'acl_action' => 'view',
                'allow_bwc' => false,
            ),
            array(
                'type' => 'rowaction',
                'css_class' => 'btn',
                'event' => 'list:delete:fire',
                'icon' => 'icon-trash',
                'label' => ' Delete',
                'acl_action' => 'delete',
                'allow_bwc' => false,
            ),
        ),
    ),
    'last_state' => array(
        'id' => 'subpanel-list',
    ),
);