The card should be redeemed to your account if you do not immediately use it in-store for a purchase. You can use it towards buying many Apple items, including the Watch you desire. To get more information about the Apple Trade In service click on the link --> Apple Trade In - Apple
- Don't miss the FAQ at the very bottom.
This article broadly outlines what you can buy with your Apple Account [Apple ID] balance --> What you can buy with your Apple Gift Card or Apple Account balance - Apple Support
• In countries and regions where Apple Gift Card is available, you can use your Apple Gift Card or Apple Account balance to buy products and accessories at apple.com, an Apple Store, or in the Apple Store app. In these countries and regions, your Apple Account balance includes the balance from any Apple Gift Cards or App Store & iTunes Gift Cards that you have redeemed.
• Buy apps, games, or in-app purchases from the App Store.
• Buy music, movies, and more from the iTunes Store, Apple TV app, or Apple Books.
• Pay for subscriptions like Apple Music, Apple Arcade, and Apple TV. Or pay for subscriptions to apps from the App Store.
• Pay for iCloud+, Apple's premium cloud subscription.
There are some exceptions, from: How apps, content, and subscriptions from Apple are billed - Apple Support
Apple Gift Card and Apple Account balance can't be used for some purchases:
• You can't use your Apple Account balance to send gifts or gift cards.
• For some recurring charges, like AppleCare+, you can't start a subscription with Apple Account balance. But as long as you keep another valid payment method on file and your Apple Account balance would cover an entire charge, a recurring charge will pull from your Apple Account balance. In some countries and regions, Apple Account balance can’t be used for some subscriptions like AppleCare+.
• Some subscriptions might not be charged to your Apple Account balance.
• If you use Family Sharing, your family members can't spend your Apple Account balance. Funds that you add to your Apple Account balance are available only to you. Learn more about how purchases bill to your Apple Account balance.