Hi Orla,
Thanks for reaching out here as well!
In my other reply, I mentioned running through our testing for conflicts procedure as a first step.
In addition, one thing you can do is to alter the total_sales custom field on the WooCommerce Product page that is associated with the ticket that you are trying to edit. You can change that number to reflect the actual number of attendees that you have, which will then change what you see in your Attendees tab.
You can also alter the ticket stock on the Edit Event page, where you edit your ticket.
Let me know how that goes!
Thanks,
Jaime