How to add a submit button in an HTML table?
Assign an id to the button and use Jquery, 
set the $idUser in a data attribute example :

 &lt;button id="buddon-id" data-user="&lt;?php echo $idUser;?&gt;" &gt;button&lt;/button&gt;
    &lt;script&gt;
    $("#button-id").on("click", function(e){
       userid = $(this).attr("data-user");
    };
    &lt;/script&gt;