What do you do if you’re at a Shabbat dinner and a person has spoken lashon harah about you before you arrived and during dinner ? Do you leave ? Do you confront them ? or Do you send an email to the people at dinner teaching them about lashon harah ?

I think the best thing is to try to forget it. Rebuke is a very difficult task and in most cases not effective, more so, in order to tell someone off you should be clean from that iniquity and you should genuinely ask yourself are you really. All the best.