Like I always tell people, don’t try to argue with them. If you can convince them that what you’re saying is true, someone else can convince them otherwise. When someone comes to Christ, it has to be God’s Spirit working in them, not clever words.
Instead, just keep loving them. By having the conversation and sharing with them, they’ll know where you stand. Live your life in such a way that it reflects Christ. And pray that God would draw them to Himself. If God is working in their hearts, He’ll provide a chance for you to share with them again.