Be completely honest. You could say, “I’ve not done one but understand the purpose of this project. It involves persuasion which I do well. I have access to samples I can draw from and know I can write this series to your satisfaction.” Be totally up front with them and then change the conversation by starting to ask questions about the project. “Tell me about this project” “What product is it for” “what will a successful outcome look like?” Remember the person asking the questions is in control of the conversation. Get really good at asking lots of questions.