Canon S450 User Manual page 290

Hold the new ink tank at a slight angle and align it with the correct slot.
5
Then insert the ink tank in its place.
Make sure you insert the ink tank into the correct slot of the cartridge
holder.
To lock the ink tank in place, press down on top of the ink tank. Press down
6
until the ink tank locks in place with a click.
Replacing the Ink Tanks
Routine Maintenance 290