Convince someone that they are on the verge of getting defrauded

How do you convince someone, that they are on the verge of getting defrauded, though you've established it is a fraud. The person is still engaging with fraudster, and it's stressing me out. How shall I steer him clear of falling for it completely, rn it's still just in talking stages. It's a crystal clear fraud, but since this person is in his mid 60's he is kinda more that half way convinced of its legitimacy.