Try this and it should help you out.

For the column add the valueFormatter property

{
headerName: "Earned", field: "revenue", sortingOrder: ['asc', 'desc'], valueFormatter: currencyFormatter
}

Use this function for the formatting

function currencyFormatter(params) {
    var usd = new Intl.NumberFormat('en-US', {
        style: 'currency',
        currency: 'USD',
        minimumFractionDigits: 2
    });

    return usd.format(params.value);
}