How to change user backend from IMAP to LDAP?

Nextcloud version (eg, 10.0.2):
Operating system and version (eg, Ubuntu 16.04): Alpine Linux
Apache or nginx version (eg, Apache 2.4.25): nginx 10.x
PHP version (eg, 5.6): 7.1


I have some users with backend = IMAP, but in our organization was integrated LDAP server and I need to move IMAP users to LDAP backend. User email (from IMAP) = user mail attribute (in LDAP).
LDAP already integrated in Nextcloud as user backend.

How can I do this without deleting users and creating new?

Best regards,