Well, your red circles are more visible.

Flat worms can change shape but they all have a similar shape. I can't tell from the pictures but even if they are flatworms, I would leave them alone. I have had infestations of flatworms before a few times and all those times, they disappeared and never hurt anything. Once there were so many flatworms I could hardly see my rock.

I personally would not add anything to eliminate them because if it has the word "eliminate" in the description of how it works, it is a poison of some type. It just depends on the dosage as to what it kills.
Flatworm exit kills flatworms and I assume all worms and a large part of the microbiome in a tank are microscope worms. But thats just me and I wouldn't use any chemical in my tank for anything that I can remember. Good Luck