If the whole lot is complete, the box should contain a small springy hook thing which you slide in twixt rack and pinion and shift over  a tooth.  You might be able to cobble something together from a sliver of beryllium copper.

I’m a bit Tom & Dick just now but will try and get a photo when I am allowed out of bed.

Martin

Afaik all the Mitutoyo dial indicators are at least similar for how the needle position is reset. But I’m not familiar with your model of dial calipers. Mine are the 505-637-50. The pinion gear is spring loaded and usually due to contamination on the rack, can skip one or more teeth. That’s what throws the needle off in most cases.

Spotlessly clean all the rack teeth first. Turn your calipers over with the back of the dial facing up, you should then see a small and narrow slot on the upper or possibly lower end of the cover that’s used to seal the rear of the calipers dial. That’s where the tip of the little tool Mitutoyo provides slides in and is used to depress the spring loaded pinion gear out of it’s engagement with the rack teeth. Basically or for my calipers, it’s just a bent piece of square wire that fits the slot in mine.

I’ve never needed to do so, but if you don’t have that tool, then most likely the plain shank end on a small drill that’s slightly narrower than the slot or hole could be used to depress the spring enough to disengage it from the rack. Or something like an opened wire paper clip might work? These videos may or may not be of help. https://www.youtube.com/watch?v=DK7W3Q85ds0 https://www.youtube.com/watch?v=Epgo_UW_s-E My calipers have the slot, but the video shows that some models of Mitutoyo calipers may need a screw removed first. You’ll have to figure out what yours require.