Cách làm: 
Bạn chỉ cần copy đoạn code sau vào bên dưới của thẻ body website : 

<div id="fb-root"></div>
<script>(function(d, s, id) {
var js, fjs = d.getElementsByTagName(s)[0];
if (d.getElementById(id)) return;
js = d.createElement(s); js.id = id;
js.src = "//connect.facebook.net/vi_VN/sdk.js#xfbml=1&version=v2.5";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>
<style>
#cfacebook{position:fixed;bottom:38px;right:20px;z-index:99;width:260px;height:auto;box-shadow:6px 6px 6px 10px rgba(0,0,0,0.2);border-top-left-radius:5px;border-top-right-radius:5px;overflow:hidden;}
#cfacebook .fchat{float:left;width:100%;height:270px;overflow:hidden;display:none;background-color:#fff;}
#cfacebook .fchat .fb-page{margin-top:-5px;float:left;}
#cfacebook a.chat_fb{float:left;padding:0 25px;width:260px;color:#fff;text-decoration:none;height:40px;line-height:40px;text-shadow:0 1px 0 rgba(0,0,0,0.1);background-image:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAqCAMAAABFoMFOAAAAWlBMV…8/UxBxQDQuFwlpqgBZBq6+P+unVY1GnDgwqbD2zGz5e1lBdwvGGPE6OgAAAABJRU5ErkJggg==);background-repeat:repeat-x;background-size:auto;background-position:0 0;background-color:#3a5795;border:0;border-bottom:1px solid #133783;z-index:9999999;margin-right:12px;font-size:18px;}
#cfacebook a.chat_fb:hover{color:yellow;text-decoration:none;}
.fchat span{ width:260px!important;}
</style>
<script>
jQuery(document).ready(function () {
jQuery(".chat_fb").click(function() {
jQuery('.fchat').toggle('slow');
});
});
</script>
<div id="cfacebook">
<a href="javascript:;" class="chat_fb" onClick="return:false;"><i class="fa fa-facebook-square"></i> Chat với LAMWEBSEO</a>
<div class="fchat">
<div style="width:250px;" class="fb-page"
data-href="/https://www.facebook.com/thietkewebsitevaseo"
data-tabs="messages"
data-width="260"
data-height="280"
data-small-header="true">
<div class="fb-xfbml-parse-ignore">
<blockquote></blockquote>
</div>
</div>
</div>


</div>
</div>

 

 

Bạn nhớ thay dòng: data-href="/https://www.facebook.com/thietkewebsitevaseo" thành facepage của mình nhé