To correct the mail, name or other data of the candidate you have to go to the "Selection Processes" menu and choose "Candidates List". From there you can directly modify the listed fields or you can click on the pencil and edit from there all the fields of the person's record.
In case the modification is to correct the mail for a candidate with tests already sent, to resend the mail with the links to the tests to a candidate, go to the process configuration (go to the "Selection Processes" menu, select "Process List", and click on the process wrench where the candidate is). At the bottom right, where the candidates are listed, select the option "View/Send Tests" where you can resend the invitation to the same registered mail of the candidate or to another mail by clicking on the resend button.