The metal tabs should line up with the holes in the plastic. It looks like the bottom tabs have been bent inward completely. You need to pull the harness out, straighten those bottom tabs to where they're perpendicular to the side of the harness. Then feed the whole harness back into place where it goes. In you picture it appears to be sitting about half an inch lower than where it should be. There are six screws to hold it, four that are flush in the top, and two that are recessed where your tabs are bent inward.
Basically, just straighten those tabs out, and line it up with the factory holes.