Step away from it and avoid engaging. Let it fade into memory. Distract yourself with something you enjoy or find fun/entertaining. Don't give them your attention or energy, and don't go looking for more stuff that will make you mad. It's hard but it does work if you stick with it and don't let yourself get stuck thinking about it over and over. If absolutely necessary, vent about it to a friend, get the salt out of your system without inviting it into your life directly. Only engage with something that you think deserves your time and energy. Just because it's a topic you give a shit about, that doesn't mean that someone being a dickhead on the internet deserves any emotional investment or emotional labour from you. Not letting yourself engage with something that upsets you can feel frustrating at first, but after a while it will begin to feel very freeing. You will start to feel less obligated to devote too much mental real-estate to things that upset you and shitty people who don't deserve the time of day from you. You will then feel less of that immediate urge to dive in and get involved in an argument, which will likely only upset you. Instead it gets easier to move on and let it fade to white noise in the backdrop of your thoughts, until it's gone completely.

That was my experience at least when I started having this issue and decided to just stop getting into it with stupid online strangers.