To run this on the regular Discord client its as simple as pressing Ctrl + Shift + I and pasting it into the console.
Sure there's a big "HOLD IT!" warning, but you're not stupid right? You can read JavaScript, right? You're not a baka... R-right?
This wont persist when you restart Discord or if you're on browser when you refresh the page. Instead of having to paste it in every time you can press Up in the console to bring up the last command.
For desktop client I recommend making a snippet in the debugger. Navigate to Sources, then next to the Page and Filesystem headers in the top right, select Snippets in the dropdown. Right click the sidebar to create a new snippet, paste the code, save it and press Ctrl + Enter to run it. This way you can easily edit the chances and not clutter up your console.
Why on earth would you want to do that?!
In the console, paste observer.disconnect(). Or simply refresh the page (on the desktop client this can be done with Ctrl + R).
Or if you're a bit dense and on the desktop client you can restart the entire thing. Better yet, restart your whole PC.