Yes, you have full control over your QnA data, just visit qnamaker.ai to make changes, you may need to sign in using your Azure login details, from the menu select My knowledge bases

You will be presented with a list of knowledge bases (if you have previously created others), click on the knowledge base that you wish to update and you will see a list of questions and answers, like this:

Where you can add, remove, or update existing questions and answers to meet your evolving needs. You can even test these changes here before you publish them.