Is there a decent guide online for replacing the cartridge slot?

I was given a couple of hand me down Nintendo 3DS XL (2012) as they aren’t reading games. They turn on and are fine in every other aspect but I’m pretty sure that the cartridge readers are just water damaged and need replacing. I can only find guides online on how to replace the ‘new’ 2015 versions of the 3DS XL though, can anyone help me out please?