To use a slotted component in a schematic, create multiple copies of the component, and give them all the same
refdes attribute. Next, select one of the components and use Edit→Edit to display the “Edit Attributes” window. If you select “Show inherited attributes”, you should see a
numslots attribute, which shows the number of slots in the package.
Select each of the copies in turn, and use Edit→Slot… to display the “Edit Slot Number” window. This can be used to set which component uses which slot in the package. When the slot is changed, gschem will automatically update the pin numbers displayed by the component.