How can I configure the applications menu in KDE?

How can I configure the applications menu in KDE (Menu -> Computer section)?

I want to add some items such as: mount and system monitor.

Updated:

What I do.

Open file .config/plasma-org.kde.plasma.desktop-appletsrc

I have this section:

[Containments][24][Applets][61][Configuration][General]
favoritesPortedToKAstats=true
icon=/usr/share/pixmaps/ubuntu-logo.png
menuItems=bookmark:t,application:t,computer:t,leave:t,oftenUsed:f,used:f
showAppsByName=true
useExtraRunners=false

And I replace with this on killed plasmashell with

[Containments][24][Applets][61][Configuration][General]
favoritesPortedToKAstats=true
icon=/usr/share/pixmaps/ubuntu-logo.png
menuItems=bookmark:t,application:t,computer:t,leave:t,oftenUsed:f,used:f
systemApplications=systemsettings.desktop,org.kde.kinfocenter.desktop,org.kde.discover.desktop,org.kde.muon,skype_skypeforlinux,org.kde.konsole
showAppsByName=true
useExtraRunners=false

I added some apps in the end of systemApplications, see code above: org.kde.muon,skype_skypeforlinux,org.kde.konsole this names I got from menu items when click to edit them, copy and paste here.

And restart plasmashell. And nothing changes.

I go to this file, and see that 1 code rewoke, and line

systemApplications=systemsettings.desktop,org.kde.kinfocenter.desktop,org.kde.discover.desktop,org.kde.muon,skype_skypeforlinux,org.kde.konsole

Disapiared tottaly.
Mabe its cached somewhere or my added apps It did not like...

Plasma 5 application menu (Kickoff)

Plasma 5 Kickoff menu is dynamic menu. It is composed from the application desktop files.

The KDE has Menu Editor:

KMenuEdit allows editing the menu of KDE application launchers.

KMenuEdit can be started either by right mouse button clicking the application launcher button on the panel and choosing Edit Applications..., or by typing kmenuedit in the KRunner line...

More from the KDE Menu Editor Handbook. Online: https://docs.kde.org/trunk5/en/kde-workspace/kmenuedit/index.html

Plasma 5.14 Kickoff Computer tab

The Computer tab applications are not editable with the KDE Menu Editor. The applications are read from the plasma configuration file. Older plasma have the 'kickoffrc' file.

As the kickoffrc was deprecated the settings were transfered to the plasma configuration file: $HOME/.config/plasma-org.kde.plasma.desktop-appletsrc.

The Computer tab applications are under the 'systemApplications'.

The user can edit the text file plasma-org.kde.plasma.desktop-appletsrc by

0) Backup the plasma-org.kde.plasma.desktop-appletsrc

1) Stop the plasmashell by executing the command (krunner): 'kquitapp5 plasmashell'

2) Edit the plasma-org.kde.plasma.desktop-appletsrc line: 'systemApplications='

3) Save the plasma-org.kde.plasma.desktop-appletsrc

4) Restart the plasmashell with the command (krunner): 'plasmashell'

KDE System Monitor (org.kde.systemmonitor.desktop) added to the 'systemApplications'

Testing with the Ubuntu 18.10 (Cosmic Cuttlefish) - Plasma 5.13

Testing done with the clean plasma-org.kde.plasma.desktop-appletsrc.

There is no 'systemApplications=' line.

Using copy and paste from https://userbase.kde.org/KDE_System_Administration/PlasmaDesktopScripting#org.kde.plasma.kickoff

Adding few more items to the systemApplications...

...seems to work BUT the 'org.kde.systemmonitor.desktop' doesn't work with the CC / Plasma 5.13 at here. The 'org.kde.systemmonitor.desktop' will disappear from the systemApplications. The 'org.kde.ksysguard.desktop' seems to work.