If you lost or deleted the email containing your reward, reach out to the sender as they can confirm the status of the reward, as well as resend if needed.
If the reward has been confirmed as sent and still does not arrive, here are a couple tips that you can do to make sure you can receive that reward:
Have the sender confirm what email address they used
Search in spam & junk for an email from email@example.com
If the message appears mark it as Not Spam or Not Junk
Create a contact for firstname.lastname@example.org in your email account
Is your inbox full?
Did you unsubscribe from email communications from this sender?
You will need to resubscribe before the sender can contact you again