When you distribute a work that includes components covered under the GPL, the GPL requires you to offer the source code to anyone who receives a copy of the binary program. Therefore, you must already offer the complete source code for your application, including the UI elements and how they are integrated into your program. If you are not already doing this, you should begin doing so immediately, because you are in violation of the GPL and are exposing yourself to legal liability for copyright infringement.
You are free, of course, to offer to teach users how to intergate those UI elements into their own programs, and you are welcome to provide such a service for a fee. The fact that you are not the author of the UI code does not preclude you from tutoring users about its use for a fee. You may also perform freelance work to modify their software to include these UI components. The users are welcome to take the source code you already gave them and try to figure it out for themselves, or they can come to you for paid explanation/work.
I would personally suggest you make it clear to users who pay for an explanation that using this UI component in their own application will carry the copyleft requirements of the GPL. If they choose to distribute their application with this component, they (like you) will need to also distribute the compelte source code for the application. You of course must include the GPL license and make it explicit that the GPL applies, but it would also be polite (and possibly more thoroughly limit your liability for fraud) to roughly explain what the GPL requires in plain English at the time you give paid instruction.