I found the instructions:
`To test this upload the file from https://raw.githubusercontent.com/nextcloud/updater/add-simplified-updater/index.php69 to /updater/index.php in your ownCloud or Nextcloud. And add the following to your config file (remove this value later after testing again!):
‘updater.server.url’ => ‘https://updates.nextcloud.org/updater_server/’,
Then switch in your admin screen to another channel and back to “stable”. You should also get a message displayed that a newer version is available. (if a warning is displayed that shell_exec is required, take a look at Test our new work-in-progress upgrader script)`