How to fix Call to undefined function get_woocommerce_currency() in wordpress?

The fix for your issue will depend on how/when you're calling those lines of code you have.

One is if you've added a hook on woocommerce_init this won't be a problem.

A very very simple example to show what I mean.

add_action( 'woocommerce_init', 'wc_init' );
function wc_init(){
    // get_woocommerce_currency() will not throw error here.
}

If you're making a plugin that should work alongside with WooCommerce, I suggest you run your plugin init inside a function hook to woocommerce_init.

I'm not really sure what you're up to. But if you're just interested in the currency, might as well just do this:

$currency = apply_filters( 'woocommerce_currency', get_option( 'woocommerce_currency' ) );
if ( 'USD' !== $currency ) {
    echo 'Hello  ';
    //my action
}

Again, working alongside with WooCommerce, you should use 'woocommerce_init' to hook your function.

update 3

function add_chalitha_shipping_method( $methods ) {
    if ( 'USD' == get_woocommerce_currency() ) {
         $methods[] = 'test_Shipping_Method';
    }
    return $methods;
}