I dumped my system using dump_bis.js, extracted it with Python2.7, and then I got a bunch of folders that start with "0100XXXXXXXXXXXX" in C:\Python27\FactoryTitles. Where is my console cert located, and how do I install it on my PC so I can use Nshoptool to deregister my account from my 3.0.0 Switch?
https://i.imgur.com/apnboXq.png
I am not sure of the exact directory, but just search for "Nshop.p12" in Windows explorer.
Once you have it just double click and it will install. You will be prompted for a password, the password is "shop". Once you have it installed open my tool and you will be prompted to select a cert, chose yours and you will be logged in on your console.
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Wow thank you very much. I had the same issue as OP when I bought a second Switch to play Mario Odyssey and other newer games. But not knowing how to unlink my account from my 3.0.0 Switch (since it's impossible to connect to eShop on a 3.0.0 Switch), I just ended up creating a brand new account at the cost of losing all the My Nintendo Points I had collected thus far. But thakns to your app, I can finally unlink my account from my 3.0.0 Switch and inherit it to my second Switch. Thank you!
No problem, glad I can help

Let me know if you got it working so I can post a guide!