If you've got a notebook with you, make a note that you need to find out, and who you have to tell, so that you actually do what you say you will. But as other

If you've got a notebook with you, make a note that you need to find out, and who you have to tell, so that you actually do what you say you will. But as others have said, I think you're overthinking this. I would far rather you tell me that you don't know but will find out, than have you make something up.