Once you complete a thread the job manager will be notified and will have three options: Approve, Reject or Return for Revision. If the thread is approved, you're done. You won't need to take it again, but you can take an additional thread from that job if the job manager didn't limit that number. Job managers can limit the number of threads a single user can take from a particular job.

If the thread is rejected, it will be returned to the pool, and you will be free to take another thread from that job (unless the job manager decided to blacklist you from her jobs).

If the thread is returned for revision, you will be requested to make changes and resubmit the thread. This can go on a number of times, depending on the patience of the job manager. In this case, you will do the thread repeatedly, each time receiving additional time to complete the thread.

Once you have submitted the thread, you cannot make changes until the job manager takes action on it and returns it to you. If the submission is rejected, that was your only chance on that thread, unless you are able to take it again after it is returned the pool.