Thank you for reaching out to the Community with your question. You definitely do have the ability to resend an email to a single contact or group of contacts through our QuickSend feature. This feature would be used on a group of less than 5 thousand contacts. Although we do not offer a one click solution to resending an email to a "Did Not Open" list of more than 5K contacts, there is a work around for this.
The first step is opening the "Did Not Open" reporting of your sent email. Once you have this list of contacts open, if you select all the contacts on the "Did Not Open" report and then choose "Manage Lists" and "Add to Lists" you can create a new list with just those contacts in it.
Once this list is created, you can then make a copy of the email you would like to resend and schedule it to go out to the new list you have created.