those look like planaria. a lot of fish will eat them and to clean them you really just have to pick them out or wipe them off and try to wipe out the infestation as you can.
welcome to FishLore! Those are generally thought to be in your tanks to a small degree all the time, but a bit of over feeding and they have a population explosion. they won't hurt your fish and most fish will eat them. But... they are a sign you need to cut the food down( a fishes tummy is the size of one eye ), gravel vacuum more thoroughly.
You can cut their numbers down by doing a couple of water changes and vacuuming each time. Good luck!
Carol
Welcome to FishLore! Sorry I don't have an answer, but, looks like you already have that. I love pics... we all do here on FishLore, so post any and all you want as much as you want.
welcome to fishlore