You can’t open another screen except Screen1, however see below…
Use the activity starter correctly… follow the documentation, chapter “Using the activity starter with two App Inventor Apps”
To pass a startup text value to the App Inventor app you are starting with the Activity Starter, ise EXTRAS to set the KEY property to the string APP_INVENTOR_START and set the VALUE Property to the text you want to pass. The other app can then retrieve this value with Get Start Plain Text
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Theoretically you also could use a startup value, check that value during Screen1 Initialize and open another screen, however in Kodular this does not work since a few years, because they never found it necessary to fix this bug [🎂 bug] Get Plain Start Text = *nothing* bug
Taifun