I removed "System Settings" app from elementary, and I tried to reinstall with the appcenter but it didn't download :( Please help me.
You can try to recompile the app, it doesn't call "System Setting", the app name is Switchboard, so just go to the Elementary OS github and check the repo of this app (https://github.com/elementary/switchboard ), 1) Download the repo 2) Install all the libraries and dependencies 3) Compile the project with vala and ninja 4) DONE ! :D
sudo apt install switchboard
and then the plugs are called things likeswitchboard-plug-sound
etc... – David Hewitt Oct 8 '20 at 14:15