Implement olark with google tag manager

Follow the step as per below link

https://www.olark.com/help/google-tag-manager

After then in your page add below google tag manager code.

your GTM-Code will be the code which is generated when you follow the steps of above link.

  <!-- Google Tag Manager -->

    <noscript>
        <iframe src="//www.googletagmanager.com/ns.html?id=GTM-Code"
                height="0" width="0" style="display:none;visibility:hidden"></iframe>
    </noscript>
    <script>
        (function (w, d, s, l, i) {
            w[l] = w[l] || []; w[l].push({
                'gtm.start':
                new Date().getTime(), event: 'gtm.js'
            }); var f = d.getElementsByTagName(s)[0],
            j = d.createElement(s), dl = l != 'dataLayer' ? '&l=' + l : ''; j.async = true; j.src =
            '//www.googletagmanager.com/gtm.js?id=' + i + dl; f.parentNode.insertBefore(j, f);
        })(window, document, 'script', 'dataLayer', 'GTM-Code');</script>


    <!-- End Google Tag Manager -->

Bleow is sample screeen of google tag manager account your GTM code is at on the top at right side.

No need to add olark code in your page.

When you follow the steps of above link ask for Site ID in custom HTML. In that case you have to create your olark account after then it will provide you Site Id.

if popup of chat still  not come then check the checkbox of "send offline message" in Settings -> Behaviour & Text