If an examiner asks, “How would you improve your research?” they’re not trying to trick you. There’s no trap in a question like, “What would you change?”
These are honest, simple questions to get you exploring the topic of what you’ve learned through your PhD journey. They might seem like questions that could only lead to more work, but they’re looking for evidence of your commitment to learning and developing, rather than a commitment to doing more for your PhD and your thesis.
You did a lot. Now you can do better.