If they have it, it should be under retraction settings. Make sure you have turned on expert mode first (File>Preferences>Print>Printing window type to Expert Mode) as that will show more settings. If there is no extra prime then I would recommend you switch to PrusaSlicer or Cura as those are the most popular slicers and they both have that setting. You will need a slicer profile for the flashforge. It is possible that the slicers come with a profile. After installing the slicer it will let you select your printer - if Flashforge is an option select it. If not, then you can search online, find a profile and import it. You can try googling Cura flashforge or prusaslicer flashforge. Here is a cura tutorial I found. Here is another discussion about this. I am not actually familiar with the flashforge, hopefully one of these works or someone familiar with it can chime in.