Rapid Developer Course 4.8 Error because of deleted attribute

Hi everyone, I am currently going through the Medix Rapid Developer Course and stumbled upon the following issues: I accidentally added the attribute´Duration´to the location, teacher, and trainee page.  Realizing this, I fixed them in the respective pages and deleted them in MyFirstModule. However, I am now receiving an error message, but only in regard to deleting the duration attribute from Trainee. Please see the following screenshot for more details: It would be amazing if someone could give me some tips how to fix this! Thanks in advance!    
1 answers

The error message exactly tells you what's the problem. The Trainee object is missing the Duration field.

The error is probably shown, because there is still a reference to that non existing field somewhere.