What do you want, exactly? Neither Discourse core nor any plugin we know of implements a dislike button that affects trust levels. If you want that, someone has to create it.
If you want someone to create it for you, I recommend posting an offer in #marketplace – your chance of the team or someone else implementing it for themselves is pretty slim because it’s a rare request.
If you want to do it yourself, you’ll have to do the hard work yourself. I’m sure you’ll get helpful responses here if you stumble over something and ask a concrete question!
If you’re looking for the source code of the Retort plugin, it’s here. If you need general help on getting started to write plugins, here’s a guide by @eviltrout.