In your account, head to the "Early Career Framework" page, where you will see listed the modules you will have to complete for the programme.
In each module, you will see a list of the self-studies. The first one is always a core self-study, and then you will see the diagnostic for each module.
By clicking "Start diagnostic", you will be able to complete the assessment. The output will be a recommendation of three self-studies to select. You are free to override this choice if you want to, but the recommendation takes into account your answers to the diagnostic questions.
You only have to complete at least three self-studies per module, but can still choose to complete more. You will see the ones you have chosen marked as with the "Selected" tag in the screenshot above.