You will see 2 ribbon cables, secured by black tabs.
Lift up the black tabs to release the ribbon cables
Push the Tensorbook chassis back into the base tray.
Fasten the base to the chassis with the screws under the keyboard
Reconnect the ribbon cables on the keyboard, then press down on the black tab to secure it in place
Slide the bottom of the keyboard into place, then push down on the top side of the keyboard
Finally, flip the machine over & fasten the two screws back into the new keyboard