When I first installed League of Legends, I occasionally had an installation package. This installation package will be placed in the folder where I downloaded it at first. If this file has not been deleted, I can find the file of this installation package and reinstall it.
If you really can't find the installation package yourself, there is no way but to download it from official website. After entering official website, click on the download game, and you will see three download methods, the first one is the speed downloader, the second one is the QQ whirlwind, and the third one is the member speed downloader. If you are a member, it is more convenient to use the third download method.
If your internet speed is suitable, you can finish the game without waiting for a long time. After the game, you should be careful this time. Put this installation package in a specific location, of course, it can't be drive C, just put it in a location that is not the hard disk of the system. This will prevent this from happening.