FOTA(Firmware Over the Air ) Update using GSM

Hi everyone
i am working on FOTA as mentioned in topic.
any one know how to do it please share ,it will help a lot with embedded advice community.
following are the conditions.
micro controllers :- esp32D/atmega2560/atmega328.
GSM module :- SIM7600EI.
Secure FOTA :- MD5 ,CRC, HTTPS ,web-server.
communication of micro controller and GSM module:- UART- RX,TX,DTR PINS.

NOTE:- I am not asking about FOTA of GSM module or firmware update.
concept is burning your micro controller hex / bin file using GSM module where bin / hex file stored on cloud or web updater.