There are 2 option to add RumbleTalk chat to your Facebook page.
The simplest way is to use RumbleTalk Facebook app.
Embed the chat in an iframe (see below)
Embed Chat in iframe
Log in to your RumbleTalk account and click on your chat name.
Click the "Get Chat Code" menu at the top left of the screen.
Choose radio button with the embed code. Copy the code in the "code" box.