There are many ways in which you can address this. Usually, whoever designs the form can anticipate that you might want to provide more information about a particular topic, and therefore, they might provide you with the chance to do so. However, if there is no designated space to provide more information, you can attach a separate piece of paper that contains this information, or contact the institution that sent you the form.
you can attach a separate piece of paper that contains this information,
Explanation:
