It means you answer the questions in the "self-assessment" yourself, honestly. You don't need a doctor for the self-assessment. If you are not comfortable that you understand the English you should ask someone to help you, but it doesn't have to be a doctor. Let's say that one of the questions is:
a) "Have you ever had any part of your lungs removed surgically?"
You should be able to answer this "Yes" or "No" without needing to talk to a doctor. Another question might be:
b) "Has you ever been diagnosed with emphysema?"
Again, you just need to remember: did any doctor ever say to you, "you have emphysema?" If a doctor has said so, you need to answer "yes." If no doctor has ever said so, then you answer "no." You don't need to have a doctor answer that question for you.
If you can answer "no" to every question, then you do not need to see a doctor.
If you have answered "yes," then they want you to consult a doctor and get a dive medical certificate.