If required, you can now lift out the lens assembly.

If you suspect dust or contamination on the sensor or IR filter you can go on from this stage to clean them without removing the lens.

The symptoms are one or more dark patches at the same place in all images and at all levels of optical zoom, but getting bigger and possibly moving out of the image on digital zoom. If the patches are fuzzy then the contamination is probably on the IR filter but if well defined, it's more likely on the sensor itself.

A video at https://youtu.be/0nmwt0frZns shows the procedure for a different but similar model of Lumix camera. One difference is that you will need a small Torx rather than cross-head screwdriver (I think T4 or maybe T3 but unfortunately I forgot to make a note of which).

With the lens removed you may be able to test the zoom by applying a 3V battery to the terminals on the bottom of the zoom motor, which is mounted on the side of the lens. Reverse the polarity of the battery to reverse the direction of motion.