Hide unused shipping providers - https://docs.woocommerce.com/document/shipment-tracking/#section-7

hide_unused_providers.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['New Zealand']);
    unset($providers['Poland']);
    unset($providers['Romania']);
    unset($providers['South African']);
    unset($providers['Sweden']);
    unset($providers['United Kingdom']);
    unset($providers['United States']); // Removes all US options
    unset($providers['United States']['Fedex']);
    unset($providers['United States']['FedEx Sameday']);
    unset($providers['United States']['UPS']);
    unset($providers['United States']['USPS']);
    unset($providers['United States']['OnTrac']);
    unset($providers['United States']['DHL US']);

    return $providers;
}

The second 'e' in Fedex should be capitalized on line 24.

In line 23 'e' should be lower case, but in line 24 'e' should be upper case:
unset($providers['United States']['Fedex']);
unset($providers['United States']['FedEx Sameday']);

Needs Poland added after line 17:
unset($providers['Poland']);

I see this code but where do I add it in wordpress to make the changes? In the functions.php file?