The silver knurled wheel must turn separately from the green balance wheel to just spin the bobbin.
a rubber disc for releasing stuck jar lids may be enough to help you get a grip on it. They can be really stuck. Oil between the sliver and green wheels. be patient. sometimes if they are really stuck I will take the needle out and put a little block of wood under the needlebar to hold the green when from spinning, but only if I a m desperate. another option and last ditch measure is to loosen the gib screw in the chrome disc, ( make sure you have a proper screwdriver, they are easy to mess up) And see if it will turn then you may need to take the chromes disc off then and oil between the washer and the diss. Don't get the 3 pronged washer in the wrong way. You will only need to turn the silver wheel about 90 degrees to get it free. Fingers crossed.