Merging an applicant to an existing employee

An internal applicant recently used a personal email address rather than the work email that was already in the system and they were offered the job but I am unable to appoint them as it creates a new record and I can't merge the records due to them using a different email and if I change the email it will delete their current record so it would be good if there was a way to be able to merge and update the email etc.