Hello!
After encountering the impossible jump past the pressure plate, you have to return to the alchemy lab room (the bottom left one in the area where you lower the walls). With the alchemy recipe book obtained, you must create Slime-Repelling Ink. A quest marker appears once you have it in your inventory, right next to the alchemy station, where you can apply the runes. Then you'll be able to cross the gap from the pressure plate.