How to unlock manually locked tasks being an administrator
1) Go the Tasks; Look for the Tasks that need to be unlocked.
only admin can unlock the tasks; if any task related to that process is locked then there will be an option in the context menu that is edit process from where a new page will get open on that page admin can unlock all tasks
2) From here you can also reassign them to other users
3) And from process history you can find out which user has locked which task and can unlock from there too.
For Bulk Unlocking Improvement https://jira.wswork.biz/browse/WIN-41523 has been rasied