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!