How to redeem my iTunes Store credit into a gift card?

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."

To me that says not in a retail store but the online store.

Apple Gift Cards (as opposed to Apple gift cards lowercase) are not available in all countries.

When you make a purchase from an Apple retail store, just show the email, then it will simply be scanned by the sales person.

It’s that easy. 

I had a recent conversation at an Apple retail store (yesterday) and I was advised exactly how it works (both online and in-store).

I have a credit balance in my apple account how can i make purchase online and in any gas station?

Your Apple account balance can be used in the App Store and Apple online & retail stores. 