On the printer under controls, there should be an option to send the XYZ Home. In the app, under device manager, control, you can press the home logo XYZ to send it back to its default location.
If the Z is not set for some weird reason, in the same area you can go in and adjust your Z position. Just be careful you don't drop the z to the point it would damage the bed.
Hope this helps
There is pre-loaded content on the printer from the card you inserted into it.
In order to print content from the app on your phone or computer, your printer must be connected to the internet and show as "online" in the app. If it is, you can then print content straight from the app by selecting the content you want, and select thebprint option.
Hope this helps.