For version 2.3.19.1 these commands use BLF-CRYPT, right? doveadm pw doveadm pw -s CRYPT

doveadm pw -l

SHA1 SSHA512 SCRAM-SHA-256 BLF-CRYPT PLAIN HMAC-MD5 OTP SHA512 SHA DES-CRYPT CRYPT SSHA MD5-CRYPT PLAIN-MD4 PLAIN-MD5 SCRAM-SHA-1 SHA512-CRYPT CLEAR CLEARTEXT SSHA256 MD5 PBKDF2 SHA256 CRAM-MD5 PLAIN-TRUNC SHA256-CRYPT SMD5 DIGEST-MD5 LDAP-MD5

doveadm pw -s BLF-CRYPT

Enter new password:

Question #2: I want to change password schema for current users. Is any way to change password schema for these accounts?

Not in some batch operation, you have no idea what the current password is, the point of hashing. All you can do is force people to change their passwords, and the mechanism that lets them change the password saves the new password with the new schema.