The user handling in openshift is handled in different kinds. I Use here the LDAP Identity Providers as example.
The official documentation describes the different back ends which are available to authenticate a users.
When a user/userin login the first time into OpenShift he/she will be created in the OpenShift users table AND in the identity table.
For example User tom001 login into openshfit.
oc login https://YOUR-LOGIN-URL --username=tom001
You will see the user/userin in the user table
oc get user tom001 NAME UID FULL NAME IDENTITIES tom001 ID tom001 LDAP:tom001
and in the identity table.
oc get identity CW-OAuth:email@example.com NAME IDP NAME IDP USER NAME USER NAME USER UID LDAP:Tom001 LDAP tom001 tom001 ID
When you now delete the user/userin from the user table the user/userin still not be able to login into OpenShift.
oc delete user tom001
When you request the user/userin again then you should get the output below.
oc get user tom001 Error from server: users "tom001" not found
The user/userin still exists in the identity table.
You will need to delete the user/userin also in the identity.
oc delete identity tom001
The user/userin will be added again into the user table and therefore the user/userin can login again into the OpenShift.