What exactly do you mean by "saving the values into datagrid"? You can't save values to a datagrid.
When your edit page loads and you bind the dropdown list, you need to find the value in the dropdownlist and mark that select item as selected. I usually do this like this:
ddlList.SelectedIndex = ddlList.Items.IndexOf(ddlList.Items.FindByValue(sS electedValue))
Peter
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Work smarter, not harder