For soft bounces, the app doesn't take an immediate action, so even if you have many soft bounces, those emails won't be blacklisted.
You can adjust these settings from Backend -> Settings -> Cron (last box in page).
If you had subscribers with many softbounces that were in the end blacklisted, then the first step is to remove them from the main blacklist. Secondly, you need to change their status from blacklisted to confirmed, and you can do this from phpmyadmin by running a sql like:
UPDATE `mw_list_subscriber` SET status = 'confirmed' WHERE `status` = 'blacklisted';