The first thing you need is the instance of Form2: the one that is being displayed.
Somewhere, you have created it, and displayed it, either using Show:
Dim f2 As New Form2()
f2.Show()
Or you are going to use ShowDialog:
Dim f2 As New Form2()
f2.ShowDialog()
In either case, you need the
f2
variable available when you want to do the copy. In the second case, that's probably trivial because you will be setting the values between the create and display of the form.
Add a Public method to your Form2:
Public Sub AddRow(row As DataGridViewRow)
myDataGridView.Rows.Add(row)
End Sub
Then call that in a loop from Form1:
Dim f2 As New Form2()
For Each row As DataGridViewRow In mySourceDataGridView.Rows
f2.AddRow(row)
Next
f2.ShowDialog()