Insert on body tag in CHILD THEME

Hi, sorry I’m not an expert, I set the child theme yesterday and as indicated by the moderator but now I’ve to insert this code:

<!– WhatsHelp.io widget –>
<script type=”text/javascript”>
(function () {
var options = {
facebook: “1797539060516164”, // Facebook page ID
whatsapp: “+393917530878″, // WhatsApp number
email: ” (Email address hidden if logged out) “, // Email
sms: “+393917530878”, // Sms phone number
call: “+3904451920702”, // Call phone number
company_logo_url: “//scontent.xx.fbcdn.net/v/t1.0-1/p50x50/13882645_1797542767182460_1306336251057963406_n.png?oh=3ce33d265bc113bfb9e6025d5e035521&oe=59FDDD17”, // URL of company logo (png, jpg, gif)
greeting_message: “Come possiamo aiutarti?”, // Text of greeting message
call_to_action: “Scrivici”, // Call to action
button_color: “#666666”, // Color of button
position: “right”, // Position may be ‘right’ or ‘left’
order: “facebook,whatsapp,sms,call,email” // Order of buttons
};
var proto = document.location.protocol, host = “whatshelp.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>
<!– /WhatsHelp.io widget –>

before the </body> tag.

How should I do this? From wordpress or from FTP client? And where to find the body tag?
Many thanks