How can I add custom js?

Hi,

I am using wp video player, but I want to customize it.

I wonder if you could help me with that.

I would like to change the js of the video like this:

var video = document.getElementById("wp_mep_1");

$(video).on({
mouseenter: function () {
video.setAttribute("controls","controls")
},
mouseleave: function () {
video.removeAttribute("controls");
}
});

How can I create an id to the video player element and conect it to this?

Thanks!