would something like this work?
on the button that navgiates you to to form2
have
submitform(form1)
If
( Not (IsBlank(form1.LastSubmit)
),
Set(varLastIt?, form1.LastSubmit)
EditForm(Form1)
Navigate(form2)
then after filling in the datacards on form 2
you hit the return button which does
Patch(datasource,Patch(datasource,LookUp(datasource, ID = varLastIt),form2.Updates)
Navigate(form1)
and then on form1 a submit form button for form1 to save