How do i fit the bobbin holder back into place

Put bobbin in holder. Thread properly. Pull out arm on bobbin which holds spool in place and gives u a handle. Place into position. Turn slightly so it fits into appropriate slot. Let go of arm. That's it. Good luck.

While I know it can only go in 1 of two ways, maybe the problem isn't in how the bobbin is in, maybe it is the route of the thread.
My assumption is you don't seem to pick up the bobbin thread and it bunches. If so the carefully follow the thread to needle you may have by passed the place you put that thread so it maintains tension.
Check that carefully, sometimes that gets overlooked.

Perhaps a video here may help:

Singer 4423 Bobbin Threading

Take off the presser foot
take off the needle plate
take off the bobbin plate
take out the needle,
clip bobbin free,
Examine the bobbin carrier on how it fits into place. (important)
Lift out the bobbin carrier.

Each machine is a little different. You may want to take pictures as you do each step for later reference. Use something like an old egg carton or a muffin tin to keep your parts from rolling around or getting knocked off an lost.

Have fun.

Have you removed the bobbin holder and then put it back in lining up the little red markings on the right hand side? If the case has moved slightly then it will keep jamming and the bobbin thread won't clear to form a stitch. The case is held in place by a magnet and a stopper but it will dislodge if you have a bad thread jam, then it keeps happening even if you have removed all the thread because its not in position.

Check this solution for image how to remove and replace the bobbin case. http://www.fixya.com/support/t9289728-bobbin_seems

When you take out the bobbin case, carefully inspect it for any damage and burrs in the black plastic, if there are any then file them carefully out with a nail file or fine sandpaper, a burr will keep catching thread too. Or you may actually need to replace the bobbin holder if it has been pierced by the needle badly, they are about $35 or so.

You may also want to get it serviced. On my 6500 during its last service the technician added a little piece that is a Janome "after sale replacement" part. It is slightly longer than the standard part, and is a little metal bit on the left hand side of the rotary hook area which is holding the bobbin holder in place better. Haven't had a major jam up since this was fitted so you may want to get this fitted on yours too.

Ok, hang on! This can get tricky! Remove the bobbin. Remove the presser foot and the needle. Remove the throat plate. This gives you plenty of room to monkey with your bobbin case. NOW, lay the bobbin case in its correct area and gently rotate it until it falls into place. It may take several tries. Once you're satisfied that it's secure, snap the holding clips into place and it should all fit nicely. THEN place your bobbin in the case correctly...check the diagram in the manual. Depending on the machine, some bobbins have the threads coming off counterclockwise and others have them coming off clockwise, but your manual should show. Sometimes, there's even a diagram on the throat plate or the bobbin case as well.
Good luck. Hope this works. If this solves your problem, please come back and rate my answer!

The bobbin fits into a bobbin case (holder), the bobbin case is what you take out to put a new bobbin in. The bobbin case fits into the hook (it has a spindle in the center) which you do not take out of the machine unless you are doing maintenance. If you just ordered a bobbin holder, it could be for another machine. you must get a case made for the machine, a generic one will not work.

When you put the hook in the pin that the bobbin case goes on should point towards you(this may work easier if you tilt the machine back slightly) it should fit in firmly then when this is in place put the locking ring in in front of it. on the bottom there is a pin that means that it can only go in one way but it can be put in backwards so be sure to put the plate on top it goes into the machine(there should be cut outs for the holders or little pins for the holders to go over) the tabs that hold the ring in place should always go from the top down and they will click in place.

Make sure the needle is in the highest position before you try putting the bobbin holder in. The bobbin holder has a metal 'finger' which fits into a 'slot' in the housing and it only goes in if you have the needle up.

Practicly impossible to "describe" how to do it, you need to be shown, other added problem is there are numerous different types of bobbins etc. Unless you can get someone to show you the next best option is to get hold of a copy of a user manual for your machine. Best of luck