Hi There,
Thanks for writing in! If you want to have a condition to display your widget like a Zendesk widget to be displayed on a specific page only, I would recommend that you use a 3rd party plugin Widget Logic. This plugin would allow you to add a condition within your widget and if the condition is meet, the widget will then display. With this plugin, you do not need a php code anywhere. You can check it here: https://wordpress.org/plugins/widget-logic/
Hope this helps. Kindly let us know.