Currently, Canvas does not support signups for student groups when making an appointment group within a particular section. This can be done if the entire class is selected, but if a section within the class is selected, the option to have students sign up as a group is not available. This is confirmed in the current documentation for appointment groups:
"Note: The groups option is only available if you previously selected the calendar for the entire course. You cannot select a calendar for a specific section because Canvas does not currently support sections in groups."
This option would be quite useful and should be implemented. There are many cases where a master site has been organized for several sections of a course, and Faculty teaching individual sections would want to set up appointment groups for their section and have students sign up as a group.