I recommend that you test all sticks together.
If that fails, then you test each stick separately in the same slot.
Once you find a good stick, then you can test all of the slots with that one good stick.
If the mobo requires other slots to be full, just test each one as you add another stick
Fill slot 1 with a good stick and test
Then fill slot 2 with a good stick and test
Then fill slot 3 with a good stick and test
Then you can move onto the other slots with other, known good sticks.