In a dashboard filter, you can specify a parameter filter text box.
If checked, this option supersedes all other values included in the Specified values option, on the Values tab of the Settings window modal. Instead, the user enters a parameter value they want to use at runtime, or search for data that matches certain values.. It creates a simple search box filter.
In dashboard Edit mode, hover over a filter that is already added to the dashboard, until the controls appear on the top right.
Click the icon (gear).
The Settings modal window appears.
In the Settings modal window, under Display Settings tab, check the following option:
Parameter filter text box appears.