Some users may have multiple accounts using different email addresses overtime. The user can choose to merge those accounts and set one account as the primary account as follows:
Login using the "primary" email and click the Account Settings:
Then, you can link additional "secondary" accounts by using the secondary email address and corresponding password:
NOTE: You cannot unlink secondary account.
Existing data of your secondary accounts won’t be affected. However, if secondary accounts is used in paper submissions and invitations after the link operation, papers or invitations will be associated to the primary account.