By going to Company > Settings > E-Mail / SMS templates you have the option to modify the text of the confirmation e-mail.
Following, an example for the salutation:
Dear SALUTATION FIRSTNAME LASTNAME IS EMPTY Dear valued customer,
IS EMPTY may not be changed. If the appointment booker did not enter the salutation, first name or last name, the term after IS EMPTY will be used as fallback, in this case Dear valued customer.
The contact fields salutation, firstname and lastname can be set as mandatory fields by going to scheduling page > contact fields and clicking on the contact field: