RadGrid EditColumn Insert Data to an Edit Field from a RadGrid in a RadWindow

I have a telerik:RadGrid that contains Bound Data,

I am calling Popup Edit Control Of RadGrid, I am getting all the fields and edit works fine.

What I want to do is from the Edit Popup, Edit one of the fields (Which is a RadTextBox) by clicking a button to open a RadWindow, this Window Contains another RadGrid with user details and one of the column with a button that executes RadGrid_OnCommand event, I am passing one of the values of the Grid by:

CommandArguments='<%# Eval("UserName")%>'

How can I place this value to the RadTextBox.Text in the Edit PopUp, So that I can update the grid with the selected value?

I would really appreciate any help. Thank you in Advance

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.