There two ways to solve this :
index.of https://cfp.kringlecastle.comas suggested in elf chat
You will find at directory listing with the file
rejected-talks.csv download it, then open using notepad or Excel(Windows) or Numbers (Mac) or any CSV online viewer like Google Sheets https://docs.google.com/spreadsheets/
then Search for the rejected talk name
Data Loss for Rainbow Teams :
Our answer is John McClane.
📟 Go to your Badge > Objectives > Enter John McClane > Submit