Consider this article from Thinking Matters in New Zealand.
There is an objection to the moral argument for God’s existence, specifically the premise which states the best explanation for the foundation for objective moral values and duties is God. It is the idea that moral values and duties can be plausibly anchored in some transcendent, non-theistic ground. That moral values and duties exist objectively, but as brute facts, not needing an explanation for their existence. They are sort of eternal unchanging ideas that are necessary features of the universe. This position we shall call Atheistic Moral Platonism, and there are three ways we could respond.
I actually used to hold to Deistic Platonism before I became a Christian, and that’s all documented in my testimony. To learn more about this topic, here is my series on how morality cannot be rationally grounded by atheism, and the series includes links to lectures and debates for further study. The relationship between a cosmic designer and objective moral values and duties is the easiest topic in the world to discuss with non-Christians. It takes only a little preparation, compared to more difficult issues like scientific evidence and the historicity of the resurrection.