To do this, first click the Manage Invitation button below the invitation on your dashboard. Then, on the next screen, click on the Add More Guests button.
Here, you''ll be able to enter in your guests' emails and then proceed to the Send page to send the invite out. You can read more on the different ways to add guests .
Note: This will send the invitation just the newly added guests. It won't resend to guests who have already been sent the invitation.