

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!
Yeah, this time it looks like you missed Steps 83-85. That's where you connect the Meeting Attendance object to the Contact object by adding a lookup field to Meeting Attendance called Contact Name.
Ok, so go to Setup > Object Manager > Meeting Attendance > Fields & Relationships and click New and then do Steps 83-85.
Then you can pick up at Step 91 again and go from there and it should work fine, ok?
Just be sure, again, to do each and every step and then there will be zero problems, ok?