1) You can use your Pro subscription on as many devices as you wish. All you need to do is log in with the exact same login method and details like the one you used to originally register with. Log out of your account on the device where you can't access your Pro account (Account Settings > Sign Out), and log in again with the account you originally used.
2) If you can't remember the method your Pro account is attached to, open Peak on the device with the Pro account, and send us an e-mail from the Help section.