Microadjusting 100-400

I have seen many threads/articles on MA a lens and am still a bit confused on how to exactly do it. I would like to MA my 100-400 lens (at the 400 end as that is what I use the most) but don't know really how to do it correctly.

Could someone pleas give me detailed instructions on how I shohuld do this?

Thank you so much for your help!