Qlik allows you to automatically make multiple selections when opening an app sheet. This is configured in the Sheet Properties using an Action:
Open the Sheet you want to configure with an action
Click Edit Sheet to enter edit mode
Click Properties
Expand Actions and click Add action
If Properties does not show the Actions tab, but instead lists Chart suggestions and other data display options, deselect the currently selected chart.
Click the drop-down arrow and choose Select values in a field
In the Field input, either search for or select the field from the drop-down
In the Value input, enter the values you want to select, separating them with semicolons (example: A;B or value1,value2)
Exit the Edit Sheet mode; this saves your changes
The defined selections will now apply whenever the sheet is opened.