I love diatonic accordion. Just have a go at it with some simple songs you know and you will find you can work it out by ear on your own.
There are some good online lessons at Liberty Bellows (USA), teaching basic to advanced.
And the Melodeon.net forum also has good advice with tuning layouts for the different instrument keys, among other topics. But it is button diatonic focused.
Hohner republished a book called “The Art of Playing Hohner Diatonic Accordions” by C. Irving Valentine. KJ Music in Australia have copies available for sale. Perhaps your local distributor can get it for you, depending where in the world you are.
Enjoy Music! Tony