I put in a new bottom hook gear but not sure how the clips go in to hold it in place

The hook and the hook driver fit together like two pieces of a puzzle. Rotate the hand wheel until the driver is on the left. Hold the hook spindle with your right hand and place it into the the hook race adjacent to the hook driver. This is easier to do with the head tilted back slightly, making it easier to see when positioning the hook and also provides stabiliity so the hook doesn't fall out. At this point, you can install the hook cover, using the keyway at the bottom of the cover to position it properly. Lock the cover in place using the latches on either side of the hook base.

the bobbin casing is not clipped in place properly, lift the lever and push in place then lower the release lever.
or try another bobbin casing, these are only 30p on Aliexpress with free shipping.

Try a couple of things first. Put in a new bobbin, and make sure it's the correct size. Replace the needle with a new 80/12. Wind the bobbin, making sure it winds evenly. (You can guide it with your fingers.)
If these changes don't help. remove the bobbin case. Clean it out, along with the hook. Remove the bottom plate, and blow out the debris with a compressor. If it still won't work, you can take it in for repair. If you do, ask them to replace the gear on the main, lower shaft. It WILL fail. Once it's replaced, you're good for another 20 years.

I was successful doing this: Take off the bottom plate. You should already have the plate & bobbin case out, place your needle where the thread should catch in the hook. Ease the toothed belt off the gear, hold it taunt so it doesn't come off the top, try not to let the gear move. With your other hand, move the race to where the hook is where you want it. Put the belt back on without moving the gear. It's easier than it sounds. Hope this helps you. I had mine all put together & then thought about taking a picture :/

Take out the bobbin and then release the hook retainer (black plastic part that the bobbin goes into), but pressing the catch on the inside left-hand-side of the bobbin door. The hook retainer should then drop and the hook can be taken out. Clean around the inside of the hook race (the circular metal part of the chassis that the hook fits in) using a cotton bud and make sure that the small groove that runs around the inside of the hook race is completely clean. Take your oil dropper and put a single drop of oil at the bottom of the hook race - you should see it 'wick' around the groove slightly - this tells you you've put it in the right place. Replace the hook, making sure its properly seated and press the hook retainer back into place firmly until the catch on the left clicks. Rotate the handwheel once to ensure that the oil is distributed and replace the bobbin. You're advised to make sure the needl is returned to the correct position for the automatic threader to work, either by pressing the needle up/down button twice or dabbing the foot controller so a complete revolution is done by the machine. You should oil the hook race every 3-5 bobbins-worth of thread. Hope that helps.

Look for articles quoting hook, base and bobbin case. Youtube is excellent on things like this. There should be a clip either side to lock the piece in place.

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.

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.

When you have that hook drive gear back out turn the wheel until the needlebar is in its highest position. The bar with the teeth that the gear fits onto should be all the way to the right. Now slide the hook driver gear back on. You can lay the hook back in and slowly turn the wheel. Watch that the point of the hook on its upwards stroke is coming slightly above the eye of the needle. When it does this you will be in the correct position to put the screw back on.
Hope this helps. It may take a couple of tries but you will figure it out.

OK, this is a general timing procedure. Loosen the screws on the main shaft gear that goes to the hook drive gear and separate the gears. Next put the needle in the left position and bring the needle all the way down by turning the handwheel. As the needle comes up make the point of the hook enter the scarf of the needle (just above the needle eye)and hold it there while you put the gears back togeather and tighten the screws. This should put it close to being in time. To fine tune it you can loosen the needle bar screw (half way up the bar that holds the needle) and adjust theneedle so the hooks point is just above the needle eye. You may have to do this a few times in order to stop it from skipping stitches. Good luck. Rick