Thanks for your question Patricia! The invitation email can not be re-sent, however, your staff members can trigger it on their own by attempting to log in with their staff email and clicking on Forgot Password. This will trigger the same email to them, where they can set their password and log in. 

Then, once they are logged in, here is the link to send them to add appointments to the calendar (if it is an appointment for a new student, they can click +New Client/Student when creating the appointment)

https://learn.thryv.com/hc/en-us/articles/15785875666317-Schedule-an-Appointment

As the admin, you should be able to view their calendars. When viewing the calendar, look in the lower left corner at the checkboxes next to their names. Check the box for a staff member to see their calendar. 

Thanks again for your post! If you run into anything else, let us know in a comment!