Change the label the Plugin Pros Table Rate Shipping plugin uses for free shipping.

trs-change-free-shipping-label.php

<?php

/**
 * Changes the label Table Rate Shipping uses for free shipping.
 * Replace NEW_FREE_SHIPPING_LABEL with the label you want to use
 * for free shipping.
 *
 * @param string           $label  Shipping method label.
 * @param WC_Shipping_Rate $method Shipping method rate data.
 *
 * @return string
 */
function trs_change_free_shipping_label( $label, $method ) {
	if ( 'wcv_table_rate_shipping' === $method->id && 0 === (int) $method->cost ) {
		$label = 'NEW_FREE_SHIPPING_LABEL';
	}

	return $label;
}

add_filter( 'woocommerce_cart_shipping_method_full_label', 'trs_change_free_shipping_label', 10, 2 );