To confirm a job appointment, call the business the day before an interview is scheduled. For example, an interviewee should call on a Friday if the interview is scheduled for Monday. Ask for the person who scheduled the interview, not the hiring manager or interviewer.
A phone call to confirm should be brief. Simply mention the reason for the call and the time and date of the scheduled interview. A professional email is also an acceptable way to confirm a job interview, especially if the bulk of the correspondence has been via email. Include all your contact information in the body of the email, so that the company can respond by phone if needed.