hack my smartphone. get root access on android 6

[znavko]

Hello! I want just to replace LowBattery.ogg in /system/media/audio/ui on my 
Android phone by Haier with my muted sound.
I cannot get root access, cause all the web contains unworkable apks and 
unacceptable exe-files.
Kongoroot, towelroor, supersu do not work, gnuroot no more maintained.
Will you help me with it?

I only tried mutter (from guix) + xserver (on android) to use android as 
display. But my knowledge and search results end there.
Phone: Tele2_Mini_1_1
Android: 6.0
How to replace that lowbattery file?