With the truss rod on the butt end of the neck you're going to have to be patient. It might takes a few goes to get it right.
Make sure you use the right size screwdriver, slowly loosen the rod and take the nut out completely.
Clean it (and the threads on the rod) and lube with some vaseline. This makes the rod adjust easier. Tighten the rod, not too much and assemble the bass again.
If that doesn't work you'll need to disassemble the bass, take the neck off again, loosen the nut, clamp the neck into a backbow and then tighten the rod. If you're lucky this should putt too much rlief into the rod and you'll have to loosen it to get it right.