1 - Open Omnichannel Administration.
2 - One the Basic details tab, copy the widget snippet code.
3 - Open the Portal Management app.
4 - In Content Snippet > Chat widge code in the web portal, paste the widget snippet code.
5 - Go to Portal > Content Snippets.
6 - Find the Chat Widget Code content snippet and open it.
Reference:
https://docs.microsoft.com/en-us/dynamics365/customer-service/embed-chat-widget-portal