The icon is a component that automatically picks up the icon from the application. When overriding the UpdateFormElements virtual method you can override the icon, when inheriting from TTMSFNCRibbonForm.
procedure TForm13.UpdateFormElements;
begin
inherited;
if Assigned(TMSFNCRibbon1Icon) then
begin
TMSFNCRibbon1Icon.Bitmaps.Clear;
TMSFNCRibbon1Icon.HoverBitmaps.Clear;
TMSFNCRibbon1Icon.DisabledBitmaps.Clear;
TMSFNCRibbon1Icon.Bitmaps.AddBitmapFromFile('MyImage.png')
end;
end;