Why do you need to reset the password? As far as I know your ATAS certificate will be sent to the email you used during application. If you have already submitted the application, you just have to wait for a minimum of 10 working days. If you were still filling-in the application and you had not submitted, I advise you just start a new application. ATAS website is NOT user-friendly. They don't even respond to e-mails.
@TreeofLife
ATAS stands for Academic Technology Approval Scheme; it's like a vetting system done by the UK Foreign Office on international students (Non-EU) who wish to pursue science/technology research courses in the UK. The idea behind is to prevent people with questionable backgrounds from pursuing courses and use knowledge gained in UK to commit terrorist activities. For instance if you're from North Korea, you won't be allowed to pursue Nuclear Engineering or related course in the UK. Without an ATAS certificate, you can't apply for student visa as it is a key requirement for many STEM research courses. Those coming to study social science courses are exempt from ATAS