<form method="post" action="options.php" enctype="multipart/form-data">
    <?php
        settings_fields("mw_options");
        do_settings_sections("mw_options");
        submit_button();
    ?>
</form>

function mw_options_wc_order_attachement_1()
{
    ?>
        <input type="file" name="mw_options_wc_order_attachement_1" id="mw_options_wc_order_attachement_1" value="<?php echo get_option('mw_options_wc_order_attachement_1'); ?>" />
        <?php echo get_option("mw_options_wc_order_attachement_1"); ?>
        <input type="submit" name="mw_options_wc_order_attachement_1" formaction="<?php echo plugins_url( 'delete_attachment.php' , __FILE__ );?>" formmethod="post" value="Delete">
    <?php
}