Putting the spring back for bobbin holder

Can be several causes. In typical probable order for rotary hook machines;
1.Top thread tension is too high (lower tension)
2.Top thread snagging at spool or elsewhere (for hoizontal spool use larger spool cap and/or machine not threaded per specific instructions)
3.Bent needle or barbed needle point (replace needle)
4.Needle not properly inserted into holder (see specific machine instructions)
5.Debris in shuttle hook/race (clean bobbin, hook, race)
6.Wrong bobbin (replace with proper machine bobbin)
7.Bobbin thread tension too high (reduce bobbin spring pressure, likewise top thread tension)
8.Poor quality or extremely light thread (if using cotton only thread, test sew with a polyester blend and see if problem goes away)
9.Bobbin case (replace bobbin case)
10.Machine timing. (check/adjust timing)
11.Burr in hook race, this can happen if a broken needle point jams in the race (remove burr or replace race)
12.Machine timing. (adjust timing)
13.Hook is worn or damaged (typically not a worn hook unless a few hundred hours of use, look for a barbed or bent hook point) Watch following Singer video... see testing top thread tension.
https://www.youtube.com/watch?v=O7N4XaIV6ms
and following animation on generic rotary hook sewing https://www.youtube.com/watch?v=zqRvljnNLFk

The hook timing is probably off. Needs to go in to the shop.

try changing the needle to see if that helps
if it doesn't,, then I suggest that the sewing machine be checked
at a repair shop to see if the bobbin case needs to be replaced and
to see if the hook and the hook race need to be replaced

The only parts that should be able to 'fall out' during shipping are the bobbin case and hook/shuttle, assuming the bobbin case was fitted in the first-place. If your machine arrived with the bobbin door open and the round black plastic hook retainer dropped down out of the hook race (on its hinge), the hook can be replaced quite simply and the hook retainer clicked back into position to retain it - you might find it easier to tip the machine back slightly when putting the hook back. If the hook retainer is still in position, just press the flat metal spring on the left of the 'U'-shaped metal retainer and the hook retainer will pop forward allowing you to put the hook in andclose back up. Make sure it clicks back into position. Does this help ???

You should have 3 pieces that make up the parts of the hook and bobbin case that you can take out to clean. 1 the bobbin case, 2 the race ring, 3 the hook. The easiest way to reinstall the hook and race ring is to tilt the machine and lay it on it's back. If you have the bobbin door open, and you rotate the handwheel and look inside the hook area, you will see the driver rotating back and forth. You want to set the hook inside the hook housing facing opposite the driver. As if your putting two halves together. Next install the race ring, shinny side out. Most of the rings have a nipple at the bottom that fits into a slot in the hook housing. Next lock the race ring in place with the 2 black or chrome arms that you swing inward. All you do next is install the bobbin case. Your done.

The plastic bobbin case should sit on top of the raceway, it should slot in quite easily, once the bobbin case is in put the small metal clip at the top over to hold it 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.

Sounds like you need to put a drop of clear sewing machine oil in the raceway of the hook. Then sew on some scrap material to soak up the excess oil.

I removed the posiotioning Plate(A). Singer Inspiration 4205. How can I get it back in?

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