Countries have different laws for gift card expiry dates. Check the laws for your country before changing this date.
Gift card expiry is defaulted to never expire. If you would like to add an expiry date to your gift cards:
Go to Settings > Gift card settings
2. Check the Gift cards expire box
3. Edit the Months field to suit your business
4. Click Save
It's a good idea to check your gift card settings in your integration gift card product also match and any mention of expiry on your website or comms is consistent.