The way to actually use confirmation bias to convince people of things is to present beliefs you want to transmit to them as evidence for things they already believe. Then confirmation bias will lead them to believe this new evidence without question, because they wish to believe it to confirm their existing beliefs.

Yep. This works pretty well, too. Useful phrases: "As you already know ..." "... and you know all this already" "I haven't told you anything you didn't know already".