Hi Christine,
Thanks for reaching out to us! I’d be happy to help you 🙂
I don’t know why that happened, but don’t worry, your events must still be saved in your database. In order to get your Events Calendar plugin back, you should reinstall it manually, via FTP.
Once you are in the wp-content/plugins folder, you should manually delete The Events Calendar, and then upload the newest version.
Have you ever used FTP? If not, this guide will teach you how to use it.
Please let me know if you need more clarification on how to procede.
Cheers,
Jeremy