Heracross doesn’t appear alone. So you need another pokemon first to make Heracross appear.
Load into Park(Night) in Florio Nature Park and head towards the first bridge. On the left side, there is a mound of dirt next to the Crystabloom.
When you scan the mound, Pinsir’s horns stick out of the ground. At this time, throw an Illumina orb at its horns to make it pop up.