Good evening Sarah and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the trouble you have run into while trying to use the Attendee data editor plugin. I would love to help you with this topic.
What is going on is that the plugin needs to be updated following our recent complete revamp of Event Tickets and Event Tickets Plus.
You will be notified as soon as the new version is out.
In the meantime, you could get this to work by downgrading both Event Tickets and Event Tickets Plus to versions 4.5.7 and 4.5.6 respectively.
I recommend reading the following: https://theeventscalendar.com/knowledgebase/downgrading-plugin-past-version/
Let me know how that goes.
Best regards,
Geoff B.