First try If the bell can be unscrewed. It is fastened with a left-hand thread, so turn it in the "wrong direction", clockwise, to loosen it.

Pull on the knife to remove it

The bell sits probably quite tight, as it should not come loose during normal operation. When reassembling, glue it in place with a few drops of fluid threadlocker, if needed.

If it does not come off easily, then slide the lower plastic part towards the bell and clamp the motor in a vice. Do not tighten the vice very much, the motor is sensitive.

Use a long screwdriver as a lever between the bell and the shaft. Then carefully unscrew the bell. Reminder: the wrong way round, i.e. clockwise.

Pay attention to the washer between the shaft and the bell, do not lose it.