There are situations when it is not possible to flash an existing module in any way.
In order to understand how to deal with this situation you need to understand how it works
BOOT mode (firmware) in the module.
The most complete implementation is made in modules with a USB connection, such as NodeMCU,
below is a diagram snippet of this module:
In this case, transistors VT1 and VT2 automatically determine the operating mode and the user does not need to do anything.
As a rule, this is very convenient for debugging modules.
If your module has minimal strapping, this is done to reduce the cost and when you don't need to sew the module on
just for experiments, most likely the scheme is something like this:
In this implementation, the BOOT mode is implemented by pulling Gpio0 to the ground using the SW1 button
This button must be held from the moment it is turned on or reset, until the firmware starts. If there is no such button in your module for some reason, it must be implemented in some way.
To work, you also need to pull up the EN pin to power and Gpio15 to ground.