I know this is a fear that many ‘newby’ presenters face. It is something that often can hold you back from speaking out, being a presenter or workshop facilitator where you are the person in the front of the room who, you believe, should know all the answers.
I suggest that you say it how it is. If you don’t know the answer, you don’t know the answer!
Have a flip chart with a page called “Parking Lot” and use this page to jot down any questions you cannot answer in the moment. Let your audience know you’ll come back to them with an answer as soon as you know. You may be able to find the answer in a break or at a time after the presentation.
Your audience will see you noting the question and will be happy to move on.
It will definitely take the stress away from you and give you time to research your answer.