If you want to update the center position of your init map on the Store Locator. You just update the value under settings.

Go to MSL dashboard > Setting > Initial State

How can I get Latitude & Longitude?

It is really simple to get the Latitude & Longitude.

Please follow the below steps.
Open https://maps.google.com/

Go to your center position which you want to display on your store locator map.

You can set zoom level based on your need.