If it gives you the option you can select the 3 dots next to the title and select "Don't recommend this channel" or "Not Interested"

I definitely hit the "Not interested" option before when a similar thing happened, but I didn't know about the other one

"Not Interested" will tell it (the Youtube Gods) that you're not interested in that particular video. So depending on why it recommended it, it might still think you're interested in Louis Rossman but just not that particular video.

"Don't recommend this channel" is like killing a fly with a nuke. It'll disappear off your home page, trending page, and side panel recommended lists. Not sure if it affects search results if you search for videos (titles) from that channel, but pretty much the only way to see videos from that channel is to search for the channel.

I'm pretty sure I've told Youtube not to recommend Louis Rossman videos as well. Definitely don't see them any more

Haha, I see. Cheers!

I got pokimane's(?) and Alinity's vids in my feed today, really odd thing, I never watch or click not only on their vids but anything remotely similar to that, so you are lucky you got Rossmann instead