You can set a dashboard filter that will be applied to all dashboard reports
To create a dashboard filter simply click on the funnel icon in the dashboard header:
Select the dimension you want to filter by from the dropdown:
Then choose the value(s) you want to include or exclude.
The available filter value will be presented in different ways depending on the number of values listed.
Once the values are selected, apply the filter by selecting the green tick and then publish those filters by selecting publish.