I dont know how to downgreat without loosing my save data can someone please explain

I think that you can't

Maybe if you take nintendo switch online there is a save in the cloud and then if you come back on the recents versions you can download your save and play (that's a supposition)

Or maybe you can download mods that allows you to save your save data with a hacked Nintendo switch, but you can't play to a 1.2.1 save data in 1.2.0, 1.1.2, 1.1.1, 1.1.0, 1.0.0.

If you have a hacked switch, you can downgrade it

Ok, how do you do it if you have a hacked switch? Can you go back to 1.1.1?

You go into the DBI App, then you can delete/install the updates for the games. I recommend you to put the updates on your SD Card, so you can install the updates when ever you want.

This gets the game back to 1.0.0. Is there any way to get to 1.1.1? I'm fine with deleting my save.

Like i said, you can have every update

HOW?

Where do you get the updates?

For legal reasons they cannot be shared here but some google searching will eventually lead you to them

Oh, you mean piracy. Nevermind.