Step 1: Login to your Zendesk Help Center admin panel.

Step 2: Go to General Settings and select Customize Design.

Step 3: Now click on the Edit Theme link on the left pane.

Step 4: Click on "JS" tab on top of the left pane.

Step 5: Paste HappyFox Chat's installation code, without the <script> tags.

Step 6: Now click "Save" and "Publish changes" button.

You are all set!