LOL, for the most part, you don't. If you have a very very good candler then you can see some things that will indicate growth or not and movement for a while at later incubation stages but you can not candle them in the same way you do other eggs. They are simply way too dark and the shells to dense.
I gave up trying to see much in them years ago. Now I just keep an eye on the aircell to see that it's growing. The latter half of incubation most of the time you can tell if there's a growing chick in it just from the darkness.
I am having the same problem with some EE and EExAustralorp eggs. The EExAus ones are a real dark olive green and impossible to see into. I am just hoping for the best. If they dont smell, they get to stay til a day or two past hatch day.