The proper response would be to laugh out loud and question the intelligence and sanity of the “reporter”, who asked the question.
Then (if you felt compelled to elaborate), go on to point out that, if you were an omniscient time traveller, you’d know all sorts of other ways to thwart the Nazis. You might also mention butterflies, and how killing baby Hitler would be akin to squashing one enormous butterfly. I could go on — but, I won’t.
A simpler, perhaps more dignified response, would be to simply say: “I don’t answer hypotheticals. Especially stupid, insane ‘gotcha’ hypotheticals. Next! Any intelligent, sane questions?”
Hmmm... puting it all on Hitler is stupid when we know it is the receptibility to Hitler’s social engineering which created the most damage. Both the liberal Germans who were for new things and Hitler were in a feedback loop.