At this time it is not possible for users to reset their library of imported listens.

In my case this had lead to incorrect data in my ListenBrainz library.

Because of the sad fact that Last.fm's system of voting to redirect faulty artist names and track titles to the correct entries has never worked properly, I frequently delete old faulty scrobbles from my library and re-scrobble them manually.

Now, every time I do an import of my scrobbles to my ListenBrainz profile, the re-scrobbled songs are added while the faulty tracks also remain in my ListenBrainz library.

After a few imports the result is that:

My Listenbrainz track count is 294,106 while Last.fm shows the actual count as 276,769.
My Listenbrainz artist count is 21,784 while Last.fm shows the actual count as 21,766.

The easiest way to solve this is to give users the option of doing a complete reset of their listens. That would enable me to import my current and correct library to ListenBrainz.