In order to revert a file (fall back to its previous version) you simply sync the previous version and submit that again.
For a single file the procedure goes like this:
# sync file at old revision (#3 in this example)
p4 sync //depot/file#3
# mark the file for edit
p4 edit //depot/file
# make perforce aware that something has to be merged
p4 sync //depot/file
# resolve (i.e. throw away the head revision changes and save those from #3)
p4 resolve -ay
p4 submit
If you have a changelist with several files (and not only edits, but also deletes & adds) the rollback is a bit more difficult.
See also this question.
Here's a smart script for that purpose and more info.
The 2nd part of your question I did not understand.
Submitting a change again with a new changelist number doesn't make sense, since a changelist contains diffs. If it was submitted once, then the diffs are already in the depot, so you can't submit the same diffs again.