As Admin user you will be able to use Question Set Editor (*If applicable and the subscription allows it) and edit any assessments that you have already on your tenant. It allows you to change the wording to questions/answers adding/removing questions and answers options and if you wish, you could create the custom Questionnaire yourself with a little help of our support team. We do recommend a training session beforehand if you do plan to make significant changes to the assessment or build your own assessment.
There is separate Guide focused on the Question Set Editor r, so please let our support team know if you need any more details about it.