Summary : This can be done right in the candidates profile.
If you have the proper role access (Recruiter, Hiring Manager, Admin, HR or Super User), you can quickly and easily change or update a candidate's email from right within their profile.
Click into the specific candidate's profile, and go to the Summary tab.
At the bottom of the Candidate Details section, click Edit.
Update the candidate's email address within the Email Address field, and click Save.
Once saved, the new email address will replace the old one moving forward
Also see: Can I Add More Than 1 Email Address to a Candidate's Profile?