How to update row of datagridview in C# not database

There are two things here - the mechanic s of adding data to a DGV programatically is simple:

myDataGridView.Rows.Add(myString, myInteger, myClassInstance, ...);

Just see here: DataGridViewRowCollection.Add Method (Object[]) (System.Windows.Forms)[^]
The other part of this is more complex - you are using a second form to supply the data, and that means you need to talk to your other form. Try this: Transferring information between two forms, Part 2: Child to Parent[^]