User login needs to go through the User data type as that is the type Bubble uses to handle credentialing.
If you already have the email and reference numbers, what you can do is:
Create User records for each of those emails either manually via CSV upload, through individual entry, or through a workflow “Create account for someone else.” The password won’t be set for this user yet.
Save the Reference number to a text field
Create a yes/no field for “Updated Password?” and set to “no” as default.
Action 2 = Log the user in > email = email input’s value, password = result of step 1
Action 3 = Update Credentials > new password = current user’s reference
Essentially you are setting the reference as their official Bubble password. Hope that helps get you in the right direction. Feel free to reach out for a coaching session at the link below if you want to work through it together!