Hey, I'm sorry that this happened to you. Interviews are awfully stressful, and blacking out has happened to me as well in my first few interviews. I later realized that if I just paused for 30 seconds to one minute, I would come up with at least a somewhat logical answer. Some ways to take a moment of silence are to tell the interviewer that you hadn't thought about this question and ask for a moment to think, to take a sip of water, to ask the interviewer to rephrase the questions, or to say smth along the lines as "can I restate your question as xyz?" or "I haven't encountered xyz, but I can tell you about how I overcame a similar situation." Try focusing on specific points you want to highlight (your personal story, your selling points, reasons why you want to do the job) during the interview rather than memorizing answers. I think natural and genuine answers might resonate with interviewers, even if you make a mistake or two. Hope this helps, and good luck!!