Be honset. It takes time to build trust. A person in this situation may have open the topic in a way simular to this:

"T, there is something that is bothering me. I am learbing how to start trusting you. But trust is not an easy thing for me. But I know being honest with eachother has to be a part of our relationship if we are going to work together.

On my intake session with you, you asked me about past trauma. I said NO. But here is the thing... I did not know you. I did not know if I could trust you. I answered that way because that is a topic too sensitive to talk about with a stranger.

You are now not a stranger. So I am ready to start talking about this with you. I will try to be as honest as I can. But I may not be able to directly answer some questions if they hit a nerve. I may need to ask for a pass on the question. But there it is."

big hugs to you!