If you participated in the crowdloan via crowdloan.moonbeam.foundation, you can return to that DApp to register your email address. A tutorial is here. You will receive an email from email@example.com within the next seven (7) days with detailed information on how to register and complete identity verification for the event.
KuCoin Participants: If you contributed to the Moonriver crowdloan through KuCoin, then you will receive instructions from KuCoin on how to join the whitelist.
Other Exchange Participants: At this time, we do not have the ability to verify your participation without help from your exchange. We are actively working to identify a solution and will provide an update if one is found.