Is possible to decompile portions of the firmware file with IDAPro.
https://github.com/pfalcon/ScratchABit was developed specifically to not recurse to proprietary tools for such kind of analysis and thus allow wider-community reverse engineering. Caveat: there's no readily available ARM Thumb2 disassembly plugin, I myself busy with REing of ESP8266 firmware (Xtensa architecture).
From https://github.com/amazfitbip/documentation/wiki/Mili_chaohu.fw :
https://github.com/pfalcon/ScratchABit was developed specifically to not recurse to proprietary tools for such kind of analysis and thus allow wider-community reverse engineering. Caveat: there's no readily available ARM Thumb2 disassembly plugin, I myself busy with REing of ESP8266 firmware (Xtensa architecture).