Log into your Joomla administration console and go to "Extensions" → "Manag" → "Install".
Press on "Upload & Install" and Upload the plugin file.
Go to "Extensions" → "Modules" . If the GetButton plugin is not in the list, click "New" button on the top left and choose the GetButton Chat Button plugin from the list. If the plugin appears in the list, click on it and visit plugin setting page.
Go to https://getbutton.io/ in another browser tab, create your button and copy the widget code from Step 3.
Go back to Joomla panel, paste the widget code into the form.
Enter the module name and check all standard plugin settings on the top right (Status, Position, Order, Menu assignment etc).