Clear it in 3 steps
Start the environment
Investigate the target
Submit the flag

This system has several cron configurations (/etc/cron.d, /etc/crontab, user crontabs, and more). Inspect each configuration file to find where the flag is written.
Check the contents of /etc/cron.d/
crontab -l shows your own crontab too
Pay attention to the arguments passed to cron job commands