This is not a difficult fix. If you are unaware of how to do it, take it to a shop.
As has also been said, if you posted in the "Luthier's Corner" or even "Setup and Repair" there might have been a lot of help already.
As to how to do this, it is really rather simple. Take the strings off the bass. Take the neck off the bass. In each of the 4 original holes in the back of the neck, drill a clearance hole (albeit a snug one) for a hardwood dowel. Glue in holes, dowel in holes, tap dowels all the way in with mallet. Let glue dry.
Sand the ends of the dowels flush with the back of the neck. Be very careful not to reduce or alter the mounting surface of the neck.
Position neck on bass and use a clamp to hold it in place. String up the E and G strings with slight tension. Just enough so the strings don't stick to the pole pieces of the pickups, but not in tune.
Adjust neck by releasing very slight pressure on the clamp. When the E and A strings are in the proper position, tighten clamp so the neck wont move. Don't go all Buckaroo Bonzai and tighten the clamp enough to crush the neck or body! Just enough to keep the neck from moving.
Now, going through the existing holes in the bass body, drill 4 pilot holes for the neck screws. Release any tension on the strings (the E and the G, remember?) and release the clamp. Put the neck plate in place and then start one screw. Get it in almost all the way. Start another screw diagonal from the first. Screw it in almost all the way.
Now put that same slight tension on the strings. make sure the neck is positioned where it needs to be, tighten the clamp again. Tighten the screws that are already in the bass and add the last 2.
Remove the clamp and string up the bass, tune/intonate and play, play, play!
If words like Pilot hole, or clearance hole are foreign terms, have someone else do it.
Also when I clamp the neck I use a bar clamp ( a larger C clamp would also work ) and I use some very dense rubber cut to sit between the fret wire and a piece of wood that has a slot in it to span a fret. This allows the clamp to do its work and not mar the finish or compress a fret.
I am unsure if there is a tutorial here, but when I re position the neck on my project bass I just might do one. Also I am probably very, um how shall I say, probably overdo it in terms of clamping and using caution, but I don't want to mess up the neck, drill through the fretboard or crush frets etc...measure 2x cut 1x is a good rule to follow!
