How to add plugin code to header html using function

How can I add this code to my header html using a function? I need to add this to a childtheme.

<!–Start of Zopim Live Chat Script–>
<script type=”text/javascript”>
window.$zopim||(function(d,s){var z=$zopim=function(c){z._.push(c)},$=z.s=
d.createElement(s),e=d.getElementsByTagName(s)[0];z.set=function(o){z.set.
_.push(o)};z._=[];z.set._=[];$.async=!0;$.setAttribute(“charset”,”utf-8″);
$.src=”//v2.zopim.com/?2viiMwgRkUnV0tYLYPgg6qcXqEgN0Gtk”;z.t=+new Date;$.
type=”text/javascript”;e.parentNode.insertBefore($,e)})(document,”script”);
</script>
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