This article explains the different kinds of gift cards Apple uses and has links on how to redeem them and what can be purchased with each kind. Click on the link --> What type of gift card do I have? - https://support.apple.com/HT204199
What you can do depends upon the country too and in your case I have no idea where you are located.
To learn 'What you can buy with your Apple ID [Apple Account] balance', click here --> https://support.apple.com/HT211187
"Where the Apple Gift Card is available, you can use your Apple ID balance to buy products and accessories at apple.com or in the Apple Store app."
For a list of countries where the Apple Gift Card is available, Click here --> https://support.apple.com/HT202631 and search for 'Apple Gift Card'
(Nov 25, 2021: the USA, Canada, Australia, and Japan)
https://www.apple.com/shop/gift-cards --> "Apple Gift Cards are solely for the purchase of goods and services from the Apple Store, the Apple Store app, apple.com, the App Store, iTunes, Apple Music, Apple TV, Apple Books, and other Apple properties." This list does not include retail Apple Stores.
While Apple Account balance can be used in the online store, I don't know if repairs count for that since they are services. In that case if you wish to double-check with Apple. I know a previous post stated (apparently definitively) that you cannot, but with a search for the terms "repair" and "maintenance" I cannot find anywhere in the documentation in the links provided where it actually says that.
Contact Apple. Click here --> https://support.apple.com/choose-country-region Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
Contact Apple for support and service --> "See a list of Apple phone numbers around the world."
Click here --> https://support.apple.com/HT201232
