So, I remember there was a plugin that was in a thread to remove black/pink outlines on Roblox images, and stupid me, I forgot to download it and bookmark it. I’ve been searching for an hour now.
This is my problem:
if you find the link to fix this it is greatly appreciated(a link to the plugin, I forgot what it’s called)
But, I read that thread already, there is no plugin. Or, can you explain how I can fix this issue in a different way?
There’s a link in it to Pixelfix, download it.
I have no idea how to use it 
There’s an entire thread explaining how to use it. I’m not sure what part you’re having trouble understanding, but here’s a couple helpful quotes from the thread:
You can grab pre-built executable files from the Github for Pixelfix.
Once you have a pixelfix executable, you can drag images onto it to fix them.
And here’s the (current) latest version on Github: Release Version 1.0.0 · Corecii/Transparent-Pixel-Fix · GitHub. You should be able to find the executable for your OS under “Assets.”
It seems to be broken now. When i send the image to it, it opens up a blank NodeJS and doesnt do anything