I don't have iView on this machine Giovanni, but I can take a fair guess.
First, if the files are already imported into LR, select them all and do Ctrl-S to save all of the metadata to file.
Then, in iView, go looking for a Sync Metadata to Files... or something along those lines!
Then, back in LR, select the files and go to Metadata > Read Metadata from Files.
That would be the theory anyway - I haven't tried it, and hopefully someone will come along who has! If you do decide to try it, usual warning apply - backup, and test on duplicates first.