How can I let staff manage appointments without administrator privileges?

Hi there.

I have many staff members, all of whom use the same facility (a planetarium) to provide their services. I need each of them to be able to manage appointments using Appointments+. Currently, to do this, I have to give all of my staff WordPress administrator privileges, which exposes my site to all sorts of risks. How can I give staff access to Appointments+ at a lower level of WP access rights?