If you used the toggle bolts that were stapled to the outside of the Unifit box, you would use a screwdriver from the top.
These are stainless steel bolts that thread into a rubber toggle.
The Toggle drops into the holes, the seat drops over them, and then the screws hold the seat down.
Many plumbers are throwing away the toggles without reading the instructions.
They need to "slow down" and do some reading.
Instruction manual for the Carlyle
Other instruction manuals
Seat toggles for the skirted bowls