List of Applications or Applications List, under GNOME, is the name given to the desktop icon showing as
Nemo should already be in there, albeit it may have a name a little different eg File Manager, or something other to distinguish it from Nautilus. If you can't find that, or be sure, go to Terminal and enter
and see what the result is.
If it is there, then all you need to do is to replace the icon for Nautilus on your Dock, and substitute Nemo.
From the Dock, you can right-click on Nautilus and choose Remove from Favourites, and it will vanish.
Then from your Applications List, once you have identified the icon and name for Nemo, you can right-click it there and choose Add to Favourites, it will then appear on your dock, and is now effectively your default FM.
Do not delete, or in any way other than that described, remove Nautilus from your GNOME Linux distribution!
Each of the DEs and their associated FMs are intimately and intricately dependent on each other. If you remove the FM, you will break the desktop. It is simpler to just shuffle the one getting replaced to be out of sight.
Cheers and Avagudweegend