<div>
    <p><?php echo esc_html__('Do you want to Confirm appointment?', 'easy-appointments');?></p>
    <form method="post">
        <input name="confirmed" type="hidden" value="true">
        <button class="button button-primary"><?php echo esc_html__('Yes, I want to Confirm appointment.', 'easy-appointments');?></button>
    </form>
</div>