There are a few different ways that you can switch between the different employers that you manage.
The easiest way is to click on the name of the current employer in the main menu.
A drop-down menu will appear showing employers you have recently accessed. You can click the employer name there to switch to it.
If you have more than 6 employers then the employer you're looking for may not be shown, but there is a link at the bottom of the list that will take you to the Employer Dashboard page where they are all listed
Click the icon in the main menu, type the first few letters of the employer name and hit return.
Then simply click on the employer name in the search results that are shown.