I solved the issue by geting the grid row, which is in edit mode so I got the value of which row I need to change and updated its Editible item by ID using this code:
var rowid = RadGrid1.EditIndexes[RadGrid1.EditIndexes.Count-1];
GridEditFormItem rowEditControls;
foreach (GridDataItem row in RadGrid1.Items)
{
if (row.ItemIndex == int.Parse(rowid))
{
rowEditControls = row.EditFormItem;
((rowEditControls as GridEditableItem).FindControl("ID") as RadTextBox).Text = e.CommandArgument.ToString();
}
}
I Hope this will be helpfull for someone, I find it valuable for customising your edit forms.