If the Questions and Responses option is enabled, the Course Questions section will appear in the admin portal. Here you can reply to users' questions, as well as edit and delete them.
Go to the Course Questions section and click the course to which a question has been set.
You will see to which content item a question has been set.
There are two ways to respond to the question. The first one is by clicking the Reply link.
The second method is to write a message to the user.
Make sure that private messaging is enabled in the account.