“I don’t understand why would need to explain to Hashem exactly how to apply his midos.”
That’s because we don’t, inasmuch as we don’t need to explain to Hashem any more so what our particular needs or feelings are; nor does the kohen gadol not wear gold because Hashem would suddenly “Remember” the cheit haeigel. (There are many many more examples of this.) Davening is beseeching to do something – there are many reasons given for why daven altogether and how it can possibly accomplish anything in terms of “convincing” Hashem to “change” His “Mind”.