Now you can replace your cleaned d-pad, A & B buttons, rubbers, and select/start rubber.
Once again reattach the FFCs to the GBA mobo, try to route the FFCs so they don’t get bent too many times or crushed by ribs and mobo etc.
Put your gold philips screws back in to the GBA mobo to hold it in place. I’ve seen some with all 3 in place, a lot only have 2, and i’ve even seen one with only a single screw!!!
Place the power switch slider into it’s slot, the shoulder button in to their slots, and the side pieces in to their slots.
Finally, reattach the GBA back shell, one black philips screw, and 6 tri-wing gold screws.