shipment_tracking.php

add_filter( 'wc_shipment_tracking_get_providers', 'custom_shipment_tracking' );

function custom_shipment_tracking( $providers ) {

    unset($providers['Australia']);
    unset($providers['Austria']);
    unset($providers['Brazil']);
    unset($providers['Belgium']);
    unset($providers['Canada']);
    unset($providers['Czech Republic']);
    unset($providers['Finland']);
    unset($providers['France']);
    unset($providers['Germany']);
    unset($providers['Ireland']);
    unset($providers['Italy']);
    unset($providers['India']);
    unset($providers['Netherlands']);
    unset($providers['Romania']);
    unset($providers['South African']);
    unset($providers['Sweden']);
    unset($providers['New Zealand']);
    unset($providers['United Kingdom']);
    unset($providers['United States']['FedEx Sameday']);
    unset($providers['United States']['UPS']);
    unset($providers['United States']['OnTrac']);
    unset($providers['United States']['DHL US']);

    return $providers;
}

add_filter( 'woocommerce_shipment_tracking_default_provider', 'custom_woocommerce_shipment_tracking_default_provider' );

function custom_woocommerce_shipment_tracking_default_provider( $provider ) {
    $provider = 'fedex'; // Replace this with the name of the provider. See line 42 in the plugin for the full list.

    return $provider;
}