As Riot Games releases more games, the company is forcing players to turn their League of Legends accounts into a general Riot Games account, so they won’t have to maintain multiple logins.
To do this, Riot has emailed players saying that they need to update their login names to something globally unique. The issue is that before this, Riot allowed overlap with login names across different regions. Note that these are the usernames you log in to the game with, not your summoner names.
This means that if you have RiftHerald as a login name in North America, somebody could still have RiftHerald as a login name in Europe, and both of the account owners are prompted to change the name. This goes for all of the League of Legends servers, including the Public Beta Environment.
If you own all the accounts that use your preferred login name, you can fix this by going to the login name change page and logging into your accounts and changing those names to something else. For example, if you wanted RiftHerald as a login on NA, you can change your other accounts to RiftHeraldPBE or RiftHeraldEUW. You can select the server (including PBE) through the dropdown menu. Once all your other names are changed, the remaining server with that login should no longer prompt you to change.
The issue is that if you had a commonly picked login name shared with other players, you can’t go and change their name, so you’ll likely have to pick a new one. There also seems to be an issue where players who use extremely obscure names are unable to keep theirs, despite not having any other League of Legends accounts in other regions. We recommend checking to see if you have a PBE account using your login name, which is a common problem for most people getting this email.
If you seem to be having this issue, you can reach out to Riot Games support and they may be able to help you unearth an account you didn’t remember you made.