For multi-location merchants, each location generally has a separate Stronghold dashboard. If a user has been given access to multiple dashboards, they can access all of them with that one user id. To toggle between each dashboard click on the merchant’s display name in the top left and select from the list of locations that will appear.
If you don't see all the locations you need access to then contact one of your company's Stronghold dashboard administrators. Your company likely has several administrators who can grant you access to all needed locations. Your company may also have some administrators who are specific to a single location and can grant access to that location.