[scribus] How do I ungroup / regroup tables?

[Kevin Cole]

How do I "ungroup" the cells of a table and then regroup after tinkering?

Actually, I want to remove the border from the left and bottom side of
the bottom-left cell of a table and the rather limited documentation I
found suggests ungrouping and regrouping.

But, when I select the table, followed by Item -> Grouping -> ..., the
available options are all disabled.