Close the lid, then flip the laptop over again.

If you reattached the bottom cover in an earlier step, remove it so you can access the internals of the laptop again.

To the right of the RAM slots, you should now see the ribbon cable for the fingerprint sensor you threaded through a hole in an earlier part of this step.

Insert the end of the ribbon cable into the motherboard and use a spudger to latch it in place.