May be difficult to find for your machine because of its age.
Something may be close on this Bernina site (the 910 looks a lot like the 930 without the basting stitch, perhaps the needle up/down function, and fewer decorative stitches):
https://www.bernina.com/en-US/Support-US/Out-of-Print-Manuals/BERNINA-manuals/BERNINA-Sewing-Systems BERNINA MATIC 910 ELECTRONIC SEWING MACHINE MANUAL CD
Most likely the machine has seized due to lack of fresh oil. The old oil has solidified and turned to glue and has stuck the moving parts together. Do not force it!
Remove the free-arm cover.
Open the top. (There is a metal peg on the top left with a screw slot in the center. Turn this screw 1/4 turn. Now lift the bobbin winder and you will see another METAL screw. Turn that 1/4 turn. Do NOT mess with the plastic screw unless you want to mess up the winder.) Now you can gently lift off the top. Pay particular attention how it fits as you will need to jimmy it a bit to get it back on without bending anything!!!
Now you can remove the cover on the left side over the needlebar.
Pick up a bottle of liquid Tri-Flow Synthetic Lube (hardware store or bike shop) with the small plastic tube dispenser. Gently rock the handwheel and apply a couple drops of Tri-Flow every place that metal rubs on metal. Do NOT oil the white nylon gears, the cams, or the belt!!! If you look closely, you will most likely see some small holes that are actually oil ports. There is a large one just on the inside of the case (left of the belt) that is part of the handwheel mechanism. This is probably where your problem exists. Do NOT over-oil or you'll be cleaning up oil for a long time and it could get into the electronics.
Work your way across the top of the machine. Be sure to move the stitch selector levers, the buttonhole knob, stitch width dial, etc and get oil into those metal mechanisms as well. There are 4 or 5 oil ports on the needlebar knuckles. Be sure to get those--one or two may be hidden so you'll need to rotate the handwheel and use the long tube to get to a couple. Oil the needlebar where it goes through the case, be sure to hit the presser foot lever mechanism.
Work your way down to the bobbin area. Be sure to get the oil port at the very back of the feed dogs next to the case (this is a very important one!). Get oil on all the metal moving parts and be sure to toggle the feed dog knob and get that mechanism too.
Now, take a handheld hairdryer and direct hot air into the internal mechanism of the machine. I've gotten the metal so warm it was difficult to touch. You may need to alternate between oil and heat, but if there is nothing mechanically wrong with your machine, this will get it running smoothly again. I've used this method on several seized mechanical Berninas and it has never failed unless a nylon gear is cracked or there is something else mechanically awry.
For sure, every time you start a project, apply a couple drops of oil where the hook and shuttle rub together (see the bottom photo below, the very bottom arrow on the left) or see page 45 of the Bernina 930 manual (Maintenance section).
Be sure to lube your machine often. Once you are familiar with the sound of a smooth-running machine, you will recognize by its sound when it needs some TLC. Other than that, plan to lightly oil every 40 hours of sewing. If in storage, every 6 months whether in use or not.
The photo below is actually a Bernina 830, but the mechanism is fairly similar to the 930/910.