This is a tough question atheists will often bring up. Philosopher Paul Copan deals with the challenge HERE.
One additional thought. I think this challenge is difficult not because it cannot be answered but because atheists don’t have the background beliefs of theism that increase the plausibility of the response. If one thinks there is no God, then almost any answer a Christian offers will seem unsatisfactory because the atheist doesn’t have a plausibility structure that allows them to give the answer a fair hearing.