You can enable it on all pages, then open page source code and copy HTML which is between "<!-- Start of Helpdesk Livechat Script -->" and "<!-- End of Helpdesk Livechat Script -->" comments. 

Then paste this code into "raw" block on the desired page.

Then disable it to not show on all pages, so it will work on the desired page(s) only.

I hope this solution should work.