The first step in repairing many printers is to remove the covers. On the Pixma IP4300, removing the cover can be frustrating because the slots are so difficult to find. Once you do find them, you should be able to disassemble the printer to get to the part you need to fix or replace.
Turn off and unplug the printer. Release the two hooks on the rear side of the printer. One is on the lower black plastic piece on the left, and the other is on the lower black plastic piece on the right. If you can't get it with your fingers, use your screwdriver.
Release the hooks on the left and right side of the main case. These are on the lower black plastic piece on each side. The screwdriver will be needed for this step.
While inserting the flathead screwdriver in the slots on the left and right sides of the printer front, release the hooks to remove the main case from the bottom case. These slots are on the bottom right and bottom left on the front of the printer with the darker grey plastic.