Eventhough this is an Access group, I'll go ahead. First check to see
that the Excel Standard Toolbar is checked by View, Toolbars. If not,
select it and the ∑ should be on it. If the Standard Toolbar is
checked, select Customize, and on the Commands tab, move to Insert and
Find the ∑. Select it with the left mouse and drag it to a tool
bar and release.