I need help to solve my urgent problem with the stm32 microcontroller

Hello . I am a university student and for the first time I am using an STM32 microcontroller. I have faced the same problem with two microcontrollers, the STM32F030C8T6 first and the STM32F103C8T6 second. The problem is as follows: I am in the process of experimenting with the sensors. When I download the code for the first time, it works normally, but when I download another code the second time, the program does not recognize it. stm32cobeide on the controller, knowing that I use st-link v2 and the computer recognizes it, but the program does not read it. Sorry for my bad English