Seasonal adjustment in SARIMA

Hi,

I am working with precipitation in California on a monthly basis. My aim is to find out which SARIMA model is the best by looking at the ACF and PACF. But before that, I have to adjust for seasonality. The series is stationary, after conducting the ADF-test.

I have looked at how other people is doing, but they are all working with not stationary series. So I don't think this method described here is working ?

https://se.mathworks.com/help/econ/nonseasonal-and-seasonal-differencing.html

Any help?