To re-send an email blast to supporters that were targeted but did not open it, you can use the following process.
First, access your Blast List and locate the blast that you want to re-send.
You can't actually re-send it, so use the 'Copy and recycle content' option to create a copy of the blast.
Now, in the new blast (the copy), you can use the following conditions in the 'Targeting' tab to accomplish the goal. It essentially says: "Target supporters that were targeted by the previous blast but who did not actually open that previous blast."