in Appointments+….can i/how do i schedule an appointment for someone who has called in to book tim

in Appointments+….can i/how do i schedule an appointment for someone who has called in to book time? i.e. i have my maintained calendar on the website…a customer calls in and books a time over the phone and pays via credit card also over the phone. How do i update the booked time for that provider in appointments+ so I do not get a double booking??