I don't use this enough to be much help but I belive this is the function you need.
Equivalent to choosing the Number tab in the Format Cells dialog box, which appears when you choose Cells from the Format menu. Formats numbers, dates, and times in the selected cells, data labels, and axis labels on charts. Use FORMAT.NUMBER to apply built-in formats or to create and apply custom formats.
Syntax
FORMAT.NUMBER(format_text)
FORMAT.NUMBER?(format_text)
Format_text is a format string, such as "#, ##0.00", specifying which format to apply to the selection.