You have to acknowledge the feelings of the other individual before they'll listen. They see themselves as good, honorable people, so you address them as such. Once you have their attention in an agreeable manner (instead of an antagonistic manner), you can address the issue at hand.

Trump did precisely this. He empathized with them and their cause. After he had an agreeable mood somewhat established, he then appealed to consequences.

If he hadn't asked them to stop, congress' attempt to reconvene would have no doubt been interrupted as well. The fact that didn't happen goes a long way against the claim that it was a call to violence.

That’s not how people work. Imagine for a second that he did come out and say that he was wrong about the fraud claims (“we looked into it and didn’t find anything”) and conceded the election. Do you honestly believe not a single one of his supporters would fall in line? There are a few people who are too far gone, but it’s entirely disingenuous to suggest he has no power over this. Not holding rallies would help a lot too. No, this is all squarely at his feet.