Official firmware for Z4 android TV is available for download. You can flash the Z4 firmware to reset the data on the android TV as well as for gaining new functionality provided by the new ROM.
Download the firmware for Z4 from here. Valid only for model with AP6335 WIFI chip.
After that follow this guide and just replace the firmware for Z4 instead of CR18. In the guide, it is explained on how to download and install drivers for windows computer. You will also need micro USB cable to connect your android TV to your computer.
Supported video formats include MKV,WMV, VC-1 SP, MP, AP, MPG, MPEG, DAT, AVI, MOV, ISO, MP4, RM, H.264, H.265, Real Video 8/9/10. Package contents include TV box, remote control, AV cable, power adapter, HDMI cable and user manual.