I would like to know, How can import my code/ project / library ( this code is from a project on a STM32L053R8 ) to make it run on my STM32F051K6T8.
I have try to import my file.c but the header which correspond doesn't get imported
You first need to install a device family pack for STM32F0 series using Pack Installer (accessible via the corresponding button in the IDE).
Then, if you already have a uVision project for STM32L053R8 then you can go to "Options for Target.." dialog and change the Target MCU to STM32F051K6T8. That should update the necessary files as well.
However, if there are any L0-specific drivers or other code in the project, those might need to be modified to properly run on an F0 device.