Update row in Form 1 after a "submit" in Form 2

Update row in Form 1 after a "submit" in Form 2

I have two forms: form1 is accessed by user1 and gets a certain number of rows written in it. Nothing uncommon there. Then, user2 acceses form2 in which he will add some rows: form2 which has a combo box lookup field to form 1 and displays some of its data. User2 needs to validate this data, add some more things and submit. After he submits, a row is created in form2, but I also need that this submit event update some columns in the associated row in form1