Hi Ripul Thakur,
Apologies for not getting back to you earlier. I've been traveling on business and then had a bit of PTO down in Florida.
The key thing with using a private github is that all the assets in the app.xml have to be "visible" to the jive instance and the app.xml. You should not have to change the app.xml.
One thing to try is resolving the app.xml's url in the browser. Also, I *think* that when you switch to a private repository, you may need to check the content type that comes across. (I can't remember where I heard this though.)
Give this a try and let me know.