Please review the instructions I copied and pasted from the Apple Support article I linked below.
>>Resend a gift
If the recipient can't find the email with the redeem button, you can resend the gift.
How to resend a gift from your iPhone or iPad
- Open the Settings app.
- Tap your name.
- Tap Media & Purchases, then tap View Account.
- Sign in with your Apple ID.
- Tap Gifts.
- Tap the gift that you want to resend.
- Make sure that the recipient's email is spelled correctly. If you need to edit the recipient's email address, tap their email address, then tap it again and enter the correct address.
- Tap Resend Gift. If you don't see Resend Gift, it has already been redeemed.<<
Gift apps, media, and more from Apple - Apple Support