You can't. The gift history only displays your first few received gifts, they really need to fix that and change them to display the latest ones.
If you're gifted when you're logged off, then you don't have any proof, but you can still contact help desk and tell them you're gift history didn't show it and they will check it for you and deal with the problem. If you are logged on, take a screenshot ASAP, because as soon as you log off, those will dissapear from your gifting history.
That's basically it.