Place the internals on top of the main cover, as shown in the photo.

You will need to push these items into the vacuum body, so having the main cover between your fingers and the engine blades is a good idea

Pop the handle vent cap back on and gently place the vacuum body over the internals

Make sure you line up the groove at the front (where the eufy logo is, see step 3) with the corresponding protrusion of the main cover

Make sure you also line up the internals correctly: the button should be right behind the button hole in the body. The battery housing though is slightly off-center, that is ok

Press the vacuum body over internals. If everything is lined up correctly, it should eventually click.

IMPORTANT: because a lot of force is required to click the main cover with the body, it is really important everything is lined up correctly so that you don't damage the device.

The on/off button will end up being pressed during the procedure. When that happens, I advise to ignore it and simply continue pushing the two halves together until the click as quickly as possible so that you can turn the vacuum off. Alternatively, turn the engine on before putting the body on it, this way it shuts down during assembly.