I agree with Vlad as for the general tips on how to behave in the interview. In case you experience stress during the interview itself, and you see this is limiting your creative thinking or structuring, the best thing to do is to:
- Recap everything you did till that moment
- Ask for one minute of time to structure your thoughts
- If still blocked/unable to find a proper answer, ask for help to the interviewer
It’s far better to ask for help if you are struggling than keep silent for 2-3 minutes without any communication with the interviewer.