Rebuilding a trip is an option that we have to "start over" with the options and choices. If you choose to rebuild, the system will start over choosing campgrounds and give you an entire new set of choices, as long as you have new filters chosen to rebuild with. (ie: tent vs RV, or pricing)
At this point, you will also have an option to keep campgrounds you already have that you "like" or "want to keep" buy locking them in place before your rebuild everything else.
Your Start and End point will always be locked so that they don't change. Any points you have added as waypoints or addresses you have added to "stop" will be locked as well so you don't lose them, unless you chose to unlock them and replace them too.