Copy and paste this code before the </body> tag on every page of your website. 

<!-- GetButton.io widget -->

<script type="text/javascript">

    (function () {

        var options = {

            call: "Mobile Number", // Call phone number

            whatsapp: "Mobile Number", // WhatsApp number

            call_to_action: "Message us", // Call to action

            button_color: "#129BF4", // Color of button

            position: "right", // Position may be 'right' or 'left'

            order: "call,whatsapp", // Order of buttons

        };

        var proto = 'https:', host = "getbutton.io", url = proto + '//static.' + host;

        var s = document.createElement('script'); s.type = 'text/javascript'; s.async = true; s.src = url + '/widget-send-button/js/init.js';

        s.onload = function () { WhWidgetSendButton.init(host, proto, options); };

        var x = document.getElementsByTagName('script')[0]; x.parentNode.insertBefore(s, x);

    })();

</script>

<!-- /GetButton.io widget -->