The individual codes can only be accessed via the coordinating teacher's user account - if you are the coordinating teacher at your school and you don't have access anymore, you can use the magic link from the confirmation e-mail you received when registering for the contest.
Once you're logged in, you can find the codes by clicking on the green bar "Find out the results of the 2020 contest" ! Alternatively, you can find the button "The Contest " on the left handside and click on "Final results". You will then be taken to the results evaluation area where the individual students are listed. In one pf the last columns you will find the personal code.
Alternatively, the code can also be found in the ranking list, which you can download as an Excel-CSV file. There you can also copy the codes and forward them to your students.