BLE Firmware update using NRF Connect SDK alongside Zephyr RTOS on VS Code.

I am trying to implement a firmware update feature via BLE to my already existing application whereby nrf52840 is connecting to an android device via BLE and is sucsessfully sending and receiving data. 

I was trying to follow this: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.3.2/zephyr/samples/subsys/mgmt/mcumgr/smp_svr/README.html#smp-svr-sample-build but I cannot figure out how to create a service where the DFU function is available just as it is possible when programming the NRF52840 using the NRF SDK without the RTOS on Segger.  I also read about the MCUBoot. I added these commands to "prj.conf" file to enable it.

CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_IMG_MANAGER=y
CONFIG_MCUBOOT_IMG_MANAGER=y

CONFIG_MCUMGR=y
CONFIG_MCUMGR_SMP_BT=y
CONFIG_MCUMGR_SMP_BT_AUTHEN=n

CONFIG_MCUMGR_CMD_IMG_MGMT=y
CONFIG_MCUMGR_CMD_OS_MGMT=y
It is also worth mentioning that I do not want to use an external flash for this project to store the image of the firmware.
In this case, the application takes longer to boot up but I cannot figure out how to make it work. Any help would be appreciated.
Thanks.