If what you meant is, how do I cleanly remove the history of an accidental checkin:
This is difficult.
svn does not allow you to undo anything since it saves revisions as changesets.
However, there are some tools, that let you do almost everything on a dump
of a repository.
You could :
dump your repo.
use one of these tools (can't remember links, but google will help)
to get rid of the checkin.
put it back into the repo.
but this course of action can completely ruin your repo, so never ever try to
do this, unless you absolutely know what you are doing and have everything backed up.
EDIT: info from comment (thx man!) and my own googlin:
svn admin tools