How to remove a zero balance gift card from my wallet

You may need to have a payment method on file, see this Apple article: Change, add or remove Apple ID payment methods

Change, add or remove Apple ID payment methods – Apple Support (UK)

See also this Apple article: Payment methods you can use with your Apple ID

Payment methods you can use with your Apple ID – Apple Support (UK)

I understand that you may want to change the country and for that, your credit balance must stand at Zero.

The options available to you are...

1. Add more funds and buy something useful else
2. Learn what to do if your remaining store credit is less than the cost of a single item.

I sent my gift card to mu friend he said it was locked and had zero balance

Can you