After you logged in, select your profile drop box and under the given options select "Report a Problem".
This will go to a page where you need to fill in a few details such as your name, email ID, and a brief about the issue you are facing. You can also attach screenshots of your issue by selecting the "Choose File" option. Once these details are filled in just select "Report Bug".
You can also visit "Help & Support" for other Hexanote related queries.