During the COVID period 19.5.2 was the only WINC that was on the market and I have updated at least fifteen to the latest fw version… so see here
https://forums.ghielectronics.com/t/atwinc1500-mr210pb1952-firmware-update-via-uart/24323
Some versions of pre-assembled modules mount a pull-up resistor on the reset line and If you connect an MPU, the reset line is high on power up before it intervenes.
The initialization sequence of the serial requires that the reset is at a low level upon power-up so remove it to update the firmware and if you want to put it back in its place at the end of the update.