Depending on the manufacturer of the processor in the device you will have to follow a different guide in order to rewrite or upgrade the firmware on your phone. Below we have separated them by chipset manufacturer that we used:
Spreadtrum based devices:
Xylo P
Mediatek based devices:
Alto S
EGO QS
Gyga QS
Gyga T
Jax Mini
Jax Q
Jax QS
Jax S
Jax X
Volt S
Volt X
Xylo Q
Xylo S
Xylo X
Xylo Z
Zun X
Zun XO
Zun XS