Primarily by engaging with others.
On can change via introspection, but others are more likely to give us non-confirmatory evidence.
Hostile discussions generally don’t lead to change.
Affection, admiration, a clear desire to please the other person, makes them more willing to listen. In that sense, Dale Carnegie was right.
If you wish to convince that something they consider is bad is morally acceptable, set it up so that they cannot respond (or do anything else) for at least 2 minutes. This gives time to weaken the “leaning” towards the affective response of disgust, and allows the rider to think more for himself.