Not Accessing Customizer

This is really a wonderful theme, I like it a lot and have used in on many websites.

On one of the websites I have a problem that many areas are not saving, therefor I am not able to access WP Customizer, this is not related to the theme. What I want is to re-install the website and correct the problem.

What I need is to know where does customizer save setting for the theme including added CSS code. So, I can get them.

Your help is much appreciated.

Thanks,