Just override the class by hook,
function woo_override_checkout_fields_billing( $fields ) {
$fields['billing']['billing_country'] = array(
'type' => 'select',
'label' => __('My New Country List', 'woocommerce'),
'options' => array('AU' => 'Australia')
);
return $fields;
}
add_filter( 'woocommerce_checkout_fields' , 'woo_override_checkout_fields_billing' );
function woo_override_checkout_fields_shipping( $fields ) {
$fields['shipping']['shipping_country'] = array(
'type' => 'select',
'label' => __('My New Country List', 'woocommerce'),
'options' => array('AU' => 'Australia')
);
return $fields;
}
add_filter( 'woocommerce_checkout_fields' , 'woo_override_checkout_fields_shipping' );
This will help you to show only 1 country in dropdown. Add this code to functions.php in theme.