During reassembly:

Guide the new Touch ID sensor's cable through its slot in the fame.

Make sure the cable is properly oriented so the press connector lines up with its socket.

Hold the cable with one hand and use your other hand to align the new sensor in its recess.

Once the sensor is aligned, gently pull the cable away from the MacBook to secure the sensor against the frame.

Continue holding the sensor in place by its cable and slowly close the MacBook.