When you add a widget, by default, it will be "No Selections".
To set value for Initial Selections, edit JSON dashboard and looks for steps, add "start": with the value. Make sure the value is available in the list.
Now, back to the UI, and check the Initial Selections
Preview the dashboard and check the initial value will be the same as the value we put in JSON.
We can do the same for Date selector. Edit JSON and looks for the related step. Below sample, if you would like to set the date range with current quarter.
This is the result when you run the dashboard, as we set in JSON, initial selection will be from current quarter to current quarter, you can change it to year, month, week, or day, or also using the absolute date.