Hi Nikhill.
How are you 'installing' it?
Are you actually installing the script as an add-on, or are you linking in the rig to a new file and the UI isn't showing?
If it's the latter, the script can no longer be automatically linked when you link in the rig, and you have to link the script in by itself, just navigate to the 'text' folder inside the file and then link or append it.
If it's the former and it's not working, is there an error message that pops up when you try?