Adding confirm step to button in Wordpress php file

I'm using a Wordpress plugin (Work The Flow) that allows file uploads / downloads / deletion etc.

The plugin allows a user to delete any file of theirs, but doesn't ask you to confirm you really want to delete it: it just immediately deletes the file.

I'd like to add in something to ensure a confirmation popup appears first.

The plugin owner pointed me to this php code in his plugin (and specifically towards btn btn-danger delete:

function getDownloadJSTemplate() {
    $script = <<<DOWNLOADJSTEMPLATE
<!-- The template to display files available for download -->
<script id="template-download" type="text/x-tmpl">
   {% for (var i=0, file; file=o.files[i]; i++) { %}
    <tr class="template-download fade">
        <td>
            <span class="preview">
            {% if (file.thumbnailUrl) { %}
                <a href="{%=file.url%}" title="{%=file.name%}" download="{%=file.name%}" data-gallery><img src="{%=file.thumbnailUrl%}"></a>
            {% } %}
        </span>
    </td>
    <td>
        <p class="name">
            {% if (file.url) { %}
                <a href="{%=file.url%}" title="{%=file.name%}" download="{%=file.name%}" {%=file.thumbnailUrl?'data-gallery':''%}>{%=file.name%}</a>
            {% } else { %}
                <span>{%=file.name%}</span>
            {% } %}
        </p>
        {% if (file.error) { %}
            <div><span class="label label-danger">Error</span> {%=file.error%}</div>
        {% } %}
    </td>
    <td>
        <span class="size">{%=o.formatFileSize(file.size)%}</span>
    </td>
    <td>
        {% if (file.deleteUrl) { %}
            <button class="btn btn-danger delete" data-type="{%=file.deleteType%}" data-url="{%=file.deleteUrl%}&action=load_ajax_function"{% if (file.deleteWithCredentials) { %} data-xhr-fields='{"withCredentials":true}'{% } %}>
                <i class="glyphicon glyphicon-trash"></i>
                <span>Delete</span>
            </button>
            <input type="checkbox" name="delete" value="1" class="toggle">
        {% } else { %}
            <button class="btn btn-warning cancel">
                <i class="glyphicon glyphicon-ban-circle"></i>
                <span>Cancel</span>
            </button>
        {% } %}
    </td>
</tr>
{% } %} 
</script>
DOWNLOADJSTEMPLATE;
return $script;
}

Can anyone advise - assuming I can create a child .php file to do this? - how I can add a confirmation stage in? The delete button can appear many times on the page, as it appears alongside each uploaded file.