I think there’s an issue with PHP version with the theme. Can you please tell us which PHP version you’re using. Basically we recommend to use PHP 7.1 or higher but it works above PHP 5.6 also. Can you please check your version & let us know? If it’s higher version of PHP then please provide a temporary admin access to your website so that we can have a look at what’s causing the issues.
You can use this plugin to provide a temporary access: