0 UserControl1
As per your comment you have a button and click of button it fires below event. Inside that method you need to create object of your second user control and call grid load method to reload your grid. See below code:
protected void Save_Click(object sender, EventArgs e)
{
UserControl2 ctrlB = new UserControl2();
ctrlB.GridLoad();
}
UserControl2
Declare a public public function which reload your grid.
public void GridLoad()
{
// Implement your own logic to load grid
gridView1.DataSource = tempList;
}