Register with Email + Password
Register using email and password, which is not tied to your Salesforce Login.
On the register page (https://app.dataimporter.io/register), you will fill in the form with the necessary information
Once you will in this information and click on Register, then you will be able to access Dataimporter.
If you register with Email + Password, then you will not be able to Log In to Dataimporter using oAuth (Salesforce Login).