Hello there,
I strongly recommend your friend to create a ticket ASAP to let the crew know of what happened - it's a lot better that you tell them before you're caught, and if there were no advantages taken from the multi account, they'll guide on how to delete the account and also document the main one for reference, as all accounts are subject to verification.
As for the deletion, your friend will have to stay off that account for at least 24h as far as I remember and then initiate a request from the homepage to delete the account - after a confirmation e-mail is acknowledged, the deletion process starts. That account will remain dormant until the end of the round for tracking purposes and a pointer will be left in the database for further reference. You can consult with T&C.
Thanks,
Gabriel
Survival of the fittest only the strong survive!