Edit the dashboard in Settings > Dashboards.
Permanent Filters
Always applied, for everyone. Viewers see Permanent filters active and can't remove them. Select ADD and choose:
By Values: a dimension and the values to include or exclude.
By Metric: dimensions and a measure.
Available Filters
Filters viewers can set themselves.
Enable Date Filter lets viewers change the dates.
Add Custom Filter adds a filter By Values or By Metric, with a Display name and, for values, a Selection Type of Single or Multiple.
[Image: The dashboard form's Permanent Filters and Available Filters sections]
Select Save or Update when you're done.