Add this to your functions files inside your child theme.

add_filter( 'woocommerce_product_add_to_cart_text', 'woo_custom_cart_button_text' );    // < 2.1

function woo_custom_cart_button_text() {

    return __( 'My Button Text', 'BELLEVUE' );

}

If you wish to change the text on the add to cart button.