How to add add code to write/read data in/from flash in peripheral_uart example

I am using a example peripheral_uart and want to implement the code where i can read the data from flash and write also. For this i have done following changes in code->

1. In prj.config ---> added line 

CONFIG_MPU_ALLOW_FLASH_WRITE=y
CONFIG_SOC_FLASH_NRF_EMULATE_ONE_BYTE_WRITE_ACCESS=y
but i get following error->
Anyone can please tell me how can i add any module/lib.
 
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