How can I remove custom CSS code in HighEnd theme?

Hello, I just had the paid for Revolution Slider plug-in installed by support at the author’s site. Below is what the support person said after he installed it. Would you be able to tell me how to remove the custom CSS he’s referring to? Thank you, Gail

“The plugin’s main admin page has some broken styles, but this shouldn’t effect the plugin’s functionality at all. To resolve the broken styles, contact your theme’s author and ask how you can remove the custom CSS that’s included in the theme that they’ve added to hide the plugin’s Purchase Code Registration section, and then this will fix the broken styles.”