The situation: You already have leads in your email campaign, and your campaign is empty with zero follow-up emails.
Since your subscribers have already subscribed to your campaign (i.e., by the automation rule you created for the funnel), you can add follow-up email sequences within the campaign (i.e., emails 1, 2, 3, etc.) and set the email delay accordingly.
Once you have done that, the first email will be sent out instantaneously (provided that you set the email delay (of the first email) in the sequence to 0). The subsequence email will be sent out depending on the email delay that you have set.