The lever is on a nearby inner wall just a few steps from the puzzle. It may highlight with alt (not sure). Even if you find the lever you will have to lockpick it.
This is difficult to explain in text. For the puzzle
every time you turn a dial all 4 parts on the dial will move 1 space clockwise. The two innermost icons will rotate into a new circle which is how you shift the symbols. You need all of the Dark circles in the lighted dial and all of the white circles on the dial on the opposite side. Once that's achieved the door will open.
