Download the Manager for Linux file from the manger.io website.
In your file manager, find the file (it’s an appimage by the way), right-click on it and look at the permissions. If necessary, tick the box to make the file executable, or alternatively if you prefer doing it in the terminal then navigate to the directory where the appimage file is located and
chmod +x Manager-x86_64.AppImage
Then double-click on the appimage file and use Manager