The Ledger hardware wallet is capable of generating a functionally unlimited number of addresses. The way you set up your Ledger, by selecting an option called the "derivation path", will change the order in which these addresses are displayed. The Ledger Live app uses a different derivation path than older apps like MyEtherWallet, but don't worry—it's safe to use either set of addresses and both can trade on RELAY.
The two main derivation paths used by apps are the newer "Ledger Live" (BIP-44) and the older "Ledger Legacy / MEW". To access your preferred addresses, you will need to select the same derivation path that you used when you set up your wallet. It's safe to use one or more addresses from both sets of paths.
In the wallet selector, click on the Ledger derivation path dropdown:
This will allow you to change between derivation paths:
Ledger Legacy (MyEtherWallet) derivation path: m/44'/60'/0'/x
Ledger Live (BIP-44) derivation path: m/44'/x'/0/0