You can't do this with a dropdown, you need to use an action to navigate between dashboards.
So create one sheet and a field called Navigation
I put it on rows and on shape to create this little sheet. This can be floated/tiled on all your dashboards.
Change the Tooltip to On Hover
Then setup dashboard actions filters.
You can create different filters for each dashboard on a single sheet.
Here is an example linking to Postal Code and Region from City
Here is the tooltip from another tab:
These will be alphabetical based on the title you give it when creating the action so number/letter if you need a certain order.
Take a look at the attached version 10 workbook. I created three dashboards and custom actions to navigate from one to another.
Navigate.twbx 1.2 MB