I want to transfer my gift card

Transfer from where?

To where?

A Gift Card can be redeemed onto an account, and once redeemed its credit cannot be returned to the card unless it has not been used at all.

You would need to contact Apple Support, to get the credit balance placed back on the card, so it can be redeemed onto another account but they will only so if the credit is unused.

iTunes Store - Contact Us - Apple Support

If that's not what you mean, you'll need to explain exactly what you want to do