First, you can export the User Account data from your existing LDAP Directory instance. This can be accomplished in many ways depending on the LDAP directory implementation. This exported User Account data (from your existing LDAP Directory) can then be uploaded into EasyIdentity using the EasyIdentity provided REST-APIs (or alternately by uploading an LDIF file of the exported data).
As for passwords, If your LDAP directory allows you to export the hashed passwords (along with hashing algorithm name), then you can export such passwords from your LDAP directory and upload them in to EasyIdentity. In addition, you can simply bulk Invite the Users uploaded into EasyIdentity to create a New Password.