Hi Dan.
Sorry this happened on your site.
It sounds like you’ll need to access your site via SFTP or cPanel File Manager or some other “files on your server” sort of access.
Then you can just delete the WooTickets folder at /wp-admin/plugins/wootickets (or, if you feel more comfortable with it, just rename it to something like “wootickets-x”)
Then try to load your site again and since the WooTickets plugin will now be deactivated, it shouldn’t be throwing that error.
You can then install and activate WooCommerce, Event Tickets, and Event Tickets Plus and you should be good to go! SeeĀ Moving to Event Tickets Plus.
Please let me know if you have any follow-up questions on this topic.