“What was your favorite part?”
You know there was one. You just need a moment to find it.
“Let me think.”
That short reply tells the other person what the silence is doing. You have heard the question, and you are considering the answer.
“Let me think. Probably the drive home. We took the long way, and the weather finally cleared.”
There is no need to deliver the whole reply at once. Finish the first phrase, take the moment you asked for, then begin your answer when you have something to say.
In everyday conversation, you can also say “Give me a second” or “I need a minute to think about that.” The first usually suggests a short wait. The second can make room for a question that needs more care.
These phrases help when your thoughts need organizing. They do not have to apologize for your English. A fluent speaker can need time to remember a place, choose a detail, or decide what they think.
The answer can be provisional, too: “My first thought is the drive home, but I might change my mind.” That gives the conversation something to work with while leaving room for a more considered answer.
Listen to the situation. A quick question about lunch needs a different amount of time from a serious question about changing jobs. If you need longer, say when you can return to it: “Could I think about it and get back to you tomorrow?”
For practice, ask yourself a question that deserves a real answer. Say “Let me think,” pause, and choose one detail. See whether the detail becomes easier to explain when you stop trying to start immediately.