If you want, tell me the exact board label or photos of the PCB/boot screen and I will suggest the most likely firmware build and the safe flashing method.
is challenging because most original units shipped with Android 4.4 KitKat and official support has ceased. However, there are community-tested "ports" and alternative firmware options available. mxq s805 firmware 51 download link
This is an unofficial port originally built for the K1 smartphone and adapted for the S805 processor. If you want, tell me the exact board
If you need to revert to a stable factory version, these are the common stock builds: : Available on AndroidPCTV . If you want