It will work even if phone doesn't get detected by SP flashtool anymore by triggering emergency brom download mode by shorting KCOL0 pin (this is present only on Mediatek SoC's).
As per MT6735P SoC documentation the logical value is 1 for the pin KCOL0. To find the pin on unknown boards, the voltage should be around 1.76-1.82v.
Please use at least 200 ohm resistor when poking around with unknown pins.
1) Remove battery of your sky 3 device and unplug it.
2) Turn on SP Flashtool to flash only preloader with a known working one and press start on the tool.
3) Short KCOL0 and ground (can be chip shielding or big copper area near scew locations).
4) Plug device to your computer. Flashing procedure should start. Stop shorting KCOL0.