Hi Marcos!
Thanks for reaching out to us! Let me try to help you with that.
Unfortunately, there is no built-in way to import attendees for an event.
The only way to generate attendees for an event would be to manually create the WooCommerce orders for them.
I did find the following thread where a user explains how you can import the CSV as orders, which in return will create the attendees for them > https://theeventscalendar.com/support/forums/topic/importing-attendees/
I hope it helps. Let me know if you have any questions.
Best,
Victor