The best place to ask questions about your certifications is to go to this discussion board on the HubSpot community or to contact HubSpot Support.
It's worth noting that most issues that students confront when trying to complete certifications is that they do not have proper permissions. Essentially, this means that features of the software are locked to them, so they cannot complete exercises.
As the Super Admin of your account, you can change your students' permissions. Read more about that here.
If you continue to have issues, you can contact HubSpot Support through the bottom right chat function. If you don't have this chat function, let us know by submitting your HUB ID here.