First check if the double entry is intentional. It is very well possible that a single person has two profiles due to, e.g., working for different organisations. Inform the participant that you would like to delete one of the profiles and ask for permission.
There are two options to merge user data from two different accounts.
One of the two options would be to transfer the registration for participation (including payments) to the other user account.
Go to: Overview => User and Participant Management => List of All Registrations for Participation
Open the profile of the corresponding participant by clicking on the full name. In the right column “Actions” click “Transfer Reg. to another User” (see Image 1).
In the segment “Select Another User for the Reassignment of a Registration for Participation” you can either choose a user with a name from the dropdown menu “New user for this participant registration” (if available) or enter the corresponding user ID into the field “User ID” (see Image 2).
Click “Preview details of new user” to make the preview appear. Check the details. You can now click on the button “confirm reassignment of registration details” and the user’s profile information will be used to overwrite the details of the participant registration (see Image 3). In that way, the participant registration will be transferred to another user. Please note that the invoice and payment will also be transferred to the "new" user account.
Don’t forget to insert the e-mail of the user that will now be deleted into the merged profile as a secondary e-mail address and check the box "Confirm validity now".
Delete the user account that now has no more role as a participant.
Go to: Overview => User and Participant Management => List of All Users
In the column “Action” click “Delete” and confirm. Please note that all submissions from the respective user must have been withdrawn. Furthermore, the user must neither be registered as a reviewer nor a PC member.