If you have already scheduled a webinar, you can invite your attendees in different ways.
Step 1 Go to My Webinar page, then you can see the scheduled webinar. Right click on the webinar or click on More and you can see a few options: Copy the Registration URL, Invite Panelist, Invite Participants:
Step 2 When you can click on Invite Panelist or Participant, it will navigate to the page below and invite by Contacts or by Emails as below.
If you choose Invite by Emails, you can enter the email address in the box and click in Invite button.
Alternatively, you can choose Default Email, Gmail or Outlook, so you can edit the email content and send out the invitation from your own email address.