How to unblock timespan?

my situation:
a tutor to mark available timespan
students to book only in marked available timespan

my thinking:
default to block full week then unblock timespan based on events marked by the tutor

I read there is “deleteMarkedTimespan” in ASPX but cannot find a similar in ASP MVC.

Here is my code in controller, but not working.

            sched.TimeSpans.Add(new DHXBlockTime()
                FullWeek = true

            foreach (var appointment in db.Appointments)
                sched.TimeSpans.Add(new DHXMarkTime()
                    StartDate = appointment.start_date,
                    EndDate = appointment.end_date,
                    CssClass = "green_section",
                    SpanType = DHXTimeSpan.Type.Default

any help appreciate. thanks in advanced.