How to enable Dates' tab for course content?

Hi everyone,
I’m trying to enable the ‘Dates’ tab to show some information about important course dates to our learners. it seems that it uses ExperimentWaffleFlag which I’m not familiar with. I added a simple waffle flag with the name course_experience.relative_dates, but nothing changed. could you help me, please?

The relating line of the code

Any help would be appreciated