Thank you for supplying your code. To SET the itemID you can use the LastSubmit property of your form.
SubmitForm(FormEdit);
Set(itemID, FormEdit.LastSubmit.ID);
Navigate(ScreenEdit_2, ScreenTransition.Fade);
Then on your 2nd screen you can PATCH like this
Patch(your_datasource_name,LookUp(your_datasource_name,ID=itemID),{your_field1: your_textinput1.Text})
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