If the computer you're connected to is connected to multiple displays, you can select which display you wish to use with Screens. To do so, use one of the following methods:
Click the Displays button in the toolbar and select the desired layout.
Navigate the Screens application menu: View > Displays > [Layout]
Remember Selected Display
In the saved screen settings, under More Settings, enable Remember selected display to automatically select the last used display for each subsequent connection.