First of all, it's important to note that you will only have an account and password if you are using a G1 WiFi Gateway in conjunction with your sensors. If you are only using SensorPush sensors directly with your mobile device(s) via Bluetooth, there is no need for an account, nor is there a way to create one.
You can reset your account login email using the web dashboard for the gateway: https://dashboard.sensorpush.com
Once you log in, go to the settings icon in the upper right where you will find the option to change the email address for the account.