You should first update your theme.
The procedure is as follows:
Go to Dashboard-> Updates
Select the checkbox next to the theme you want to update(or check a “Select all” checkbox to update all themes)and then click “Update Themes”.
Do same for the plugins.
If, after that, the theme customization is still not working, please describe what the exact problem is and give me your login information to your site in the private reply, so that I can check what’s happening.