I have selected Riley to reset her password but when I click on the button to reset it, nothing happens.

Sorry you're stuck but there's almost always a pretty easy fix! Do NOT try to start all over again, uninstall Max's Pitch Package, etc. That can make it worse. There's a 95% chance the same snag/fix is listed & answered in the Help FAQ. But if you can't find it there, post your problem here.
Make sure you post in the right category below & be sure to include a screencap showing the issue!
I went to a different browser and the pop up worked.
My guess is that the email you set for Riley back in Lab 3a wasn't a valid email address so the reset email isn't going anywhere. Got to Setup > Users > Users > Riley Morgan and look at the email address set for her (not the username). That is where the reset emails are being sent. If that's not a real address, you need to click Edit and set it to a real one you can check and Save. But the new address won't show up until you get the confirmation email at that new address and click on the confirmation link. Only then will the new address be set for her. After that the pw reset email will go to that address.
Let me know, ok?