Once you unlocked your Pixel Pack, for example by redeeming a pre-order code, you should be able to find the new content in-game. If you need help redeeming a code on your platform, have a look at this article.
 
For the Pixel Pack, these are the items that are added to your game:
 
We put together detailed information on the Season Pass in a dedicated article - please have a look.

If you are unsure where to find the items that are included in the pack you unlocked, please check out this article.

Finally, if you would like more information about sharing content on Nintendo Switch, feel free to visit this article.