Hey @emmanang,
If your client has a valid purchase for the official currency converter widget you can contact WooCommerce.com support for that. Have you’re client as you as a collaborator on their account by following these steps below if you’re not already a collaborator.
https://docs.woocommerce.com/document/adding-collaborators/
You’ll then be able to use your own WooCommerce.com customer account to submit support requests on behalf of your client.
https://woocommerce.com/my-account/create-a-ticket/
Before submitting a support request I’d suggest carrying out a quick conflict test on the staging site as JavaScript issues can usually be due to a code conflict of some kind.
You can test on your site by disabling all other plugins aside from WooCommerce along with switching to a theme like Storefront. This will help with trying to and locate what software you have installed which could possibly be causing this behaviour? You could use a free plugin called Health Check and Troubleshooting to carry out such testing.
When in Troubleshooting mode all plugins will be deactivated and only the admin of the site carrying out the troubleshooting would see those changes. Any customers visiting the site would see no changes at all.
Once you have disabled all other plugins and switched theme if the behaviour is resolved you can then enabled your theme and sites plugins testing after each one is enabled until the behaviour returns to locate the culprit.
https://docs.woocommerce.com/document/how-to-test-for-conflicts/