Coordinates aren’t required for your Local SEO schema, but they can help pinpoint an exact location for your business.
To get the latitude and longitude for your business’ location, you can use this resource from laatlong.net. Once you have both, you can then enter it in on the JM Simple Small Business Local SEO settings page.
And if you don’t want to add in the coordinates for your business, don’t worry. Those items won’t appear in the JSON-LD output if you leave both of them blank.