Its important to try to siphon out as many as you can before doing flatworm exit. When those little buggers die they do release a toxin and you want to remove any dead ones floating after you FWE your tank. As many as you can see there are as many or more under rocks, in your pipes and elsewhere. FWE will kill all of the living ones potentially nuking your tank. I would siphon out any that you see and repeat for a day or two before doing the FWE treatment. A simple 3/8" tube from your display that leads to your sump that has a fine mesh bag at the end works great to siphon out the FW's without removing water from the tank. You can siphon all day that way and not worry about extra buckets or dumping water.
The follow up FWE treatments are just to kill any that hatch. Large water change and fresh carbon after each FWE treatment.
So, you can:
1. Do FWE a couple times and they all should be gone in a few weeks
2. Get a wrasse to control the population. They will never be gone.
Or you can do both. I wouldn't bother breaking down and restarting. Its not that major of an issue if controlled. They don't do any harm in your tank unless they are covering your LPS and suffocating them from light.