TLDR; Its takes less than 5 minutes - you have to simply copy paste the script in the website header.
Step by step instructions:
(1) In your Gleen dashboard, go to Settings screen and click on Integrations

Configure under the Website Chat Support
Installation tab. Copy the js code and paste it before the body tag:
Customize the Widget’s logo, name and color:
You can change everything about the widget by going under Customize Homescreen and Customize Messenger tabs:

