You can located dashboards in the library's dashboard overview and using the picker on an individual dashboard.

Dashboards in the library

In the Dashboard library you can filter dashboards by searching for the name or owner. You can also filter by category, or by Recent, Bookmarked, Certified and those owned by you or shared with you.
Dashboard library with Recent filter selected

Dashboard picker

On individual dashboards, you can select dashboards from a list. The three most recently viewed dashboards are at the top of the list. Select the Change dashboard icon next to the a dashboard's title and search for the dashboard you want to see.
Dashboard search list with highlighted Change Dashboard icon