esp32 to transmit bin file/data to other MCU

[Chocomilky]

In one of my project I have two MCUs, where one is esp32 and the other is stm32.
They both communicate with each other via UART.
And esp32 receives and can save the received binary file/data into one partition first. And what I want to do is to transmit the binary data from a partition to stm32 via UART so that stm32 can get updated.
Is there any example or api calls for the case?

Any help will be appreciated.
Thanks.