Hi,
It does not seem broken. I guess it is a Landeron movement. If it is the case, anyway parts are easy to find and are not expansive.
If the stem has just come off because the setting lever was no longer well screwed, it is a very easy fix. If something broke in the keyless system it will require more work.
In both cases, if the watch has not been serviced for a long time, it could be a good idea to give it a full service.
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