Electrics often are designed to have a slight warp. The slight warp keeps light strings from buzzing. If the action is good and the notes are true, don't adjust it.

If you are adjusting it, loosen the strings, pull the neck back (bracing between your leg) and tighten the nut a bit. Let the pressure off the neck, then pull it back and tighten it a tiny amount. Be patient. Do it a bit at a time. It works. I once straightened a severely warped Fender bass this way.