When someone has already made a decision, there still might be a way to get them to reconsider.
Get them to reconsider? Get them to rescind that decision?
How do you get someone to reconsider a recent decision?
Find out who he made the decision with?
Ask them what it will take to get them to reconsider?
Give them a reason to reconsider? (Better features, benefits, values, experiences, price).
Get them to doubt the soundness of the decision?