@jojo2338 It is actually very simple, friend.
First, go to qbittorrent and pause the torrent.
Then, go through your hard drive and look for the files to make sure you really have them.
As soon as you find the files, check the directory they are in.
Go back to qbittorrent, check the download location in the general tab of the torrent file. Example: 
If the directory where you found the files matches the directory reported as the "Save Path" then all you need to do is simply right-click the torrent and select "Force Recheck" and just wait for it to finish.
Because it is a HUGE torrent, performing a recheck can take hours!!! The more files you have, the longer it will take to finish.
After performing the recheck, if the client reports that your torrent is not 100% complete, it can be because some files are corrupt or they were not found in the download path.