When you add a table, its placeholder name (Table 1, for example) is hidden by default. You can show the name and edit it. No tables in a presentation can have the same name.
Do one of the following:
In the table, Control-click the row number for row 1, then choose Show Table Name or Hide Table Name.
Click the Table tab at the top of the sidebar on the right, then select or deselect the Table Name checkbox.
If you don’t see a sidebar, or the sidebar doesn’t have a Table tab, click 
in the toolbar.
With the table name showing, do any of the following:
Change the table name: Triple-click the name, then type a new one.
Enclose the table name in a border: Click the Table tab at the top of the sidebar on the right, then Select the “Outline table name” checkbox.
If you don’t see a sidebar, or the sidebar doesn’t have a Table tab, click in the toolbar.