Does anyone know how to get Gemini to help refactor code? I’m trying to paste in my code file and the web page says “an error has occurred” and the code does no

Does anyone know how to get Gemini to help refactor code? I’m trying to paste in my code file and the web page says “an error has occurred” and the code does not show up in the code window. I tried signing up for Gemini Advanced and that didn’t help. I also tried pointing it to the file on GitHub and it said it couldn’t access it. People here are saying Gemini is great for code refactoring. How do you do that?