Duolingo is not that great when it comes to explaining certain expressions. "Não interessa como" is the same as "não me interessa como", meaning literally "(it) doesn't interest me how". It's commonly used when someone (your boss, for example) asks you to do something, and he doesn't care how you do it. So he would say "Eu quero isto pronto até o meio-dia, não interessa como" (I want this done by noon, doesn't matter how). "Não importa como" is also used with the same meaning.
It does not matter how.
But seriously, I've encountered many cases in Duolingo where an idiom is presented and I have a hard time translating it using the hover hints. The hover hints are there to help you out, but in the end, you just need to learn the expression. It sucks that you have to lose a heart when you mess it up the first time, though.
Actually I don't mind losing a heart at all. Once in awhile I have to go back and repeat a lesson. But it's all part of the learning process. I can usually figure out from the comments if an expression is really widely used or just a clumsy computer-generated sentence.
It doesn't matter how is exactly it! Purists will disagree but if you speak to someone in their own language and get it wrong, they will not rebuke you or roll around the floor laughing, they will appreciate you trying, being understood is the priority fine tuning comes later. It is more use speaking a lot poorly than speaking very little perfect.