If you really lack experience in this area, then you have to give a smart answer to this question. If you already have the experience in this area, then you just need to provide proofs and justifications.
Sample answer is:
I have strong interest in working on this area. So I have already completed two online courses in this domain to gain the required knowledge. I understand that there will be a learning curve. To make it shorter, I am willing to spend extra time on this area. Based on my previous experience of working on domain, I can pick up things quickly over here. I am sure I can be a valuable contributor in these areas within a short span of time.