Howto read the owncloud.log file? - didn' understand previous answer

My problem is the same as in this post:
Howto read the owncloud.log file?
How am I supposed to read the owncloud.log log file? As I understand, the log file is json encoded and is a technical format - not made for human reading. But the given answer doesn't help me or I do not understand. It is written there: "this can be read from your admin user backend", but my user backend does not have any display of logfile-content. When looking at Settings... Administration... General... Log... there are only two lines: one with a dropdown-field to choose, what kind of information should be in the protocol (which is set to "errors and fatal problems" at the moment) an a second line with a button "download logfile".
And I don't find an app named "logreader" in the market.

Server configuration

Operating system: ubuntu 16.04

Web server: Apache/2.4.18 (Ubuntu)

Database: mysql Ver 14.14 Distrib 5.7.19, for Linux (x86_64) using EditLine wrapper

PHP version: PHP 7.0.22-0ubuntu0.16.04.1 (cli) ( NTS )

ownCloud version:

Updated from an older ownCloud or fresh install: upgraded from 10,0,0,12, but problem was the same in some older versions

Where did you install ownCloud from: packet source for ubuntu 16.04

Output from

No errors have been found.

The content of config/config.php:

    "system": {
        "updatechecker": false,
        "instanceid": "ocjm2jb6whjw",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
        "datadirectory": "\/var\/www\/owncloud\/data",
        "overwrite.cli.url": "http:\/\/\/owncloud",
        "dbtype": "mysql",
        "version": "",
        "dbname": "oc",
        "dbhost": "localhost",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "logtimezone": "Europe\/Berlin",
        "installed": true,
        "overwriteprotocol": "https",
        "maintenance": false,
        "mail_from_address": "u.dahms",
        "mail_smtpmode": "php",
        "mail_domain": "",
        "theme": "",
        "loglevel": 3,
        "enable_previews": true,
        "memcache.local": "\\OC\\Memcache\\APCu",
        "filelocking.enabled": true

List of activated apps:

  - activity: 2.3.6
  - announcementcenter: 1.2.0
  - calendar: 1.5.4
  - comments: 0.3.0
  - configreport: 0.1.1
  - contacts: 1.5.3
  - dav: 0.3.0
  - federatedfilesharing: 0.3.1
  - federation: 0.1.0
  - files: 1.5.1
  - files_external: 0.7.1
  - files_pdfviewer: 0.8.2
  - files_sharing: 0.10.1
  - files_texteditor: 2.2.1
  - files_trashbin: 0.9.1
  - files_versions: 1.3.0
  - files_videoplayer: 0.9.8
  - firstrunwizard: 1.1
  - gallery: 16.0.2
  - market: 0.2.2
  - notifications: 0.3.1
  - provisioning_api: 0.5.0
  - systemtags: 0.3.0
  - templateeditor: 0.1
  - updatenotification: 0.2.1
  - encryption
  - external
  - files_antivirus
  - theme-example
  - user_external

Are you using external storage, if yes which one: no

Are you using encryption: no

Are you using an external user-backend, if yes which one: no

You could download the log file and use an editor like sublime to make looking through the log file easier.

Okay, this would be a way. But nevertheless I would like to know, how I can look at the last logfile entries (errors) directly from the admin user backend - which should be possible, as it was written in that post. What can I do to use this functionality inside the user backend?