Function only works on page refresh

I’ve written the following function to change currencies depending on a form submission.

 if($from=="Antrim" || $from=="Armagh" || $from=="Down" || $from=="Fermanagh" || $from=="Derry" || $from=="Tyrone"){

$mycountry ="GB";

}

else{
    $mycountry ="IE";
}

add_action( 'wc_price_based_country_before_frontend_init', 'my_function', 10, 1 );
function my_function($mycountry) {
  
   return $mycountry; 
}
    
  if(wcpbc_set_woocommerce_country($mycountry)){
   echo"wcpbc_set_woocommerce_country($mycountry) Success;";
  }
  else{
    echo "wcpbc_set_woocommerce_country($mycountry)  Failed";  
  }
my_function($mycountry); 

The output of the script is wcpbc_set_woocommerce_country(GB) Failed and the currency is not updated.

However, if I refresh the form data or add another order the output is still wcpbc_set_woocommerce_country(GB) Failed

But the currency has been updated to £.

Any idea what I’m doing wrong?