I didn't want to leaving you hanging with nothing. If you are using Chrome, go to your inactive users page. Right click near the grid of users, hit Inspect. Go to console on the little window that pops up. 
Copy and paste this into the console line.

var str = "Email Address, Last Login\r\n";$("table > tbody").children().each(function(){str += $($(this)[0]).text().replace(/(\r\n|\n|\r)/gm,"").replace(/\s+/g, ",").substring(1)+"\r\n";});window.prompt("Copy to clipboard: Ctrl+C, Enter", str);

Hit enter. You should see a window pop up. You can copy and paste this into a file and call it, "inactive_users.csv". You should be able to open this file in Excel. You can also just paste it into a word processor or notepad. I have included a video of how to do this. 
https://www.carbonitex.net/share/howtoexportinactive.mp4