How to put balance back on to gift card?

You can’t transfer your Apple Account balance to another payment method. From the article below.

About unused Apple ID balance

You can't redeem or return Apple Gift Cards, App Store & iTunes Gift Cards, or unused Apple ID balance for cash, except as required by law. If your jurisdiction allows for refund of redeemed gift balances, you can contact Apple Support to request a refund. - When you contact Apple, please include the following information:

Your Apple ID.   -

The refund amount.

Your current shipping address.

Apple ID balance - View  *

You need a zero account balance and you need to cancel all your subscriptions. If you have cancelled all subscriptions, but some haven’t expired, contact iTunes Support. You need a valid credit card issued by a bank in the country the store is in and you need a billing address in that country. If you have an account balance, either buy something more expensive and pay the balance with a credit card or contact iTunes Support and ask them to zero balance your account.

Purchases - View, change, or cancel your subscriptions.      *

How to cancel Apple TV+.  *

Purchases - Subscriptions not billed through Apple    *

Link to contact Apple Support at the end of the article.

Purchases - the subscription that you want to cancel is not listed    *

Region - Change your iTunes Store, iBooks Store, or App Store country or region.     *

If you have done all the above and are still having problems, contact iTunes Support. See the Apple Support articles below for contact information.   

iTunes Support – world wide   -

Apple Support schedule phone call     -

Billings and Subscriptions   -

Apple on Twitter  - 

Not if you want to change the region the App Store/iTunes is in. You can spend the balance in your current region.

You are welcome.