From your My Webinars dashboard, select your webinar to bulk register attendees.
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Select the Registration tab.
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Bulk Registration supports uploading a .csv file to bulk register attendees. There is a sample downloadable file on the Bulk Registration page. The sample CSV file is dynamically generated based on the registration form.

While uploading, you are provide the option to send registration confirmation emails. And if you had an attendee register with an incorrect email, you may update their information using the 'Update existing records' option'.