Hi Rafael,
This guide was written to help you migrate users from one IdP to another.
Since your users originally existed as local users, I believe this “backward” migration will be possible. However, it’s worth noting that users created from an initial SAML login will have random numbers appended to their logins in the SQ database, and you will not be able to migrate them.
HTH,
Ann
P.S. Would you mind sharing why you’d like to migrate back to the in-app authentication? We don’t consider its use best-practice.