The Not Opened by metric may not appear in your account by default. Poppulo Support must manually enable it, and can only do so for an account which has Whitelisting set up. Once enabled, then you can Resend to People Who Did Not Open.
In the event that the Not Opened By figure does not display in your Overview Report, and you want to find those who didn't open your email, you can still do that by using a Metric Search to Search for Non-Engaged People, Tag People using a Metric Search, and from there you can choose to Resend an Email.
