How to transfer my iTunes gift card.....to another account

You can't do this yourself. Click here and ask the iTunes Store staff to put it back onto the card; they'll only do this if none of the balance has been spent.

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You can send a gift in the amount of the credit from one Apple ID to another Apple ID.

Send iTunes Gifts - Apple Support

iTunes Store credit can't be spent on gifts. Trying to do that will either fail completely or result in the amount in question being charged to a credit card.

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