Check the diameter - is it roughly 13+mm? I think there’s only two sizes, with 13mm being the larger of the two and the other between 9 and 10mm. You are looking for a battery hatch/cover for a Swatch Irony. I would ask in a dedicated Swatch outlet first but generally a few on eBay.
Example:
https://www.ebay.co.uk/itm/305499914...Bk9SR_6PwIqMZQ