Register at developer.nintendo.com, download the free tools, and off you go. Switch development is much more straight forward than previous Nintendo consoles. You'll need a dev console eventually which will cost a bit, but you can get quite far before spending anything.
I'd -gladly- write games (and software) for the switch if it was a more accessible platform to develop for.
Developing software for Nintendos previous platforms was difficult for anyone who didnt have 'connections' in the industry.