You can retrieve the password by visiting the BITSAT website and  click on forgot password, fill the details as asked and you will get your password . If you still didn't get the the Bits password you can contact the the bits exam board through email or their contact details they have provided in their official website.

The contact and mail details of bits board are

Admissions Office, BITS, Pilani - 333 031 (Rajasthan) India.

Sorry to know this. But don't worry you can retrieve the password by visiting the BITSAT website and just click on Forgot password. Fill the details asked and you will get your password retrieved. If your problem don't solve by this way then I would recommend you to contact the BITS authority and get your problem informed they will surely resolve your problem or will guide you out.

As per the official website the contact details are:

Admissions Office, BITS, Pilani - 333 031 (Rajasthan) India.
Tel: 01596-242205, 01596-255294, 01596-255330 Fax: 01596-244183

I hope this answer helps. All the very best for your future endeavors!