If it's a conventional clasp its should be possible to adjust the snap action by carefully bending in the right place, I do this frequently on old watches to get a nice clasp action. However, I don`t recommend doing this unless you're confident, it's all to easy to make it worse. Working out where to bend is the tricky part. Can`t give any more advice without seeing the thing in detail, but unless something's damaged and needs replacing this isn`t a Zenith-specific issue to sort out.