how can i add an additional action into woocommerce admin order page through my plugin?

You can use this code to add an action on the admin order page:

const CUSTOM_ACTION_CODE = "my-plugin__custom-action-code";


add_filter("woocommerce_order_actions", function ($actions) {

    $actions[CUSTOM_ACTION_CODE] = "label of the custom action";

    return $actions;

});


add_action("woocommerce_order_action_" . CUSTOM_ACTION_CODE, function (\WC_Order $order) {

    // here the code of the treatement of $order
    //...


});