Since it was messed with before you worked on it, one thing you can try is heating up the extruder and checking to see if the nozzle can be tightened up anymore. There could be material in the nozzle threads preventing it from screwing all the way on when cool.Otherwise, you have to go to the thread - "Sticky: Flashforge Creator Dual / Pro How to fix Dual Extruders dragging across prints" and follow the instructions there to adjust the extruder height even with the other one.