bought gift card for someone and they don't have an apple product

The Apple Support article: Check your Apple ID balance - https://support.apple.com/HT202359 says:

"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 [ https://support.apple.com/contact ] to request a refund."

You can speak with Apple to see what your options are:

Click here --> https://support.apple.com/choose-country-region/media-services 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

There's various options but you do not provide us with any additional information so we then have to just start guessing.

Yes, iTunes for Windows is one; if you or your friend have a Windows machine.

Apple Music for Android is another.

Finding an online gift card reseller is another.

Giving it as a gift to somebody else who can use it is another.

And so on...

Hello,

Another option may be for them to use iTunes for Windows which should allow them to redeem gift cards to use for iTunes contents.

Download and use iTunes for Windows - Apple Support

I hope this helps.