You can do that why the "Reseed" procedures.
In principle, you load the torrent into qBittorrent and on the window which will show to confirm the download location, you will have to navigate to the folder (aka directory) which contains the former µTorrent downloaded data. Then run a recheck.
You might need to set the qBittorrent graphical user interface options to show that window. I recommend as well to change qBittorrent's setting not to start downloading a newly added torrent immediately.
Note that on Windows, I've noticed a small but important difference between µTorrent and qBittorrent: In µTorrent you have to select the file or folder from which the torrent was created. In qBittorrent you have to select the folder which contains the file or folder from which the torrent has been created.
A more basic reseed procedure is described in the English FAQ.