If someone missed one or more emails in an automation, or you want to send an email associated with an automation to a contact who isn't in the campaign, you can!
From the automation, click the campaign email you want to send.
Now, click Quick Send and choose the contact you wish to send it to.
If you use Quick Send, it will add the individual to the exclusion list, meaning if they end up in the automation, they will not receive it again
If the person has already received this email and you are intentionally sending it again, it will be sent.