public void changeUserPassword(String username, String oldPassword, String newPassword) {
    byte[] encodedNewPassword = encode(newPassword);
    ModificationItem[] mods = new ModificationItem[1];
    mods[0] = new ModificationItem(DirContext.REPLACE_ATTRIBUTE, new BasicAttribute("UnicodePwd", encodedNewPassword));

String base = "OU=someOtherOU,OU=someOu,DC=domain,DC=dom";
String userCN = "CN="+username;
String userDN = userCN + "," + base;
    LdapContextSource contextSource = new LdapContextSource();
    contextSource.setUrl("ldap://my-domain.com:389");
    contextSource.setBase(base);
    contextSource.setUserDn(userDN);
    contextSource.setPassword(oldPassword);
    contextSource.afterPropertiesSet();

    LdapTemplate ldapTemplate = new LdapTemplate(contextSource);

    ldapTemplate.modifyAttributes(UserCN, mods);
}

private byte[] encode(String password) {
    String quotedPassword = """ + password + """;
    char[] unicodePassword = quotedPassword.toCharArray();
    byte[] passwordArray = new byte[unicodePassword.length * 2];
    for (int i = 0; i < unicodePassword.length; i++) {
        passwordArray[i * 2 + 1] = (byte) (unicodePassword[i] >>> 8);
        passwordArray[i * 2] = (byte) (unicodePassword[i] & 0xff);
    }
    return passwordArray;
}