Are the spots showing as a dull area against a shiner back ground? If so then simply apply another coat of paint.
If not then you will need to re-spackle the affected spots, sand and prime with Kilz or Zinsser Cover Stain. The primer is available in quarts or spray cans for small areas. With a real primer you will be able to easily see if the spots are good and if not continue to work on them.