How can I implement the Buttonless DFU feature? (SDK12.3, nRF52832)

I am implementing a buttonless_DFU function right now.
I decided to do Buttonless on my project's PCB Board because it is no longer an environment where I can add switches.
I read the project source at C: \ nRF5_SDK_12.3.0_d7731ad \ examples \ ble_peripheral \ experimental_ble_app_buttonless_dfu \ pca10040 \ s132 \ arm5_no_packs, but the scenario is too hard to understand.
If it's not difficult, can you explain the scenario?
Keep it simple
If you have difficulty, you should make the chip state in what environment, and what kind of logic is enough to solve it easily.
I tried to merge example sourece with source in my existing project, but it takes a lot of trouble instead of one or two.

Can't I add fds function to bootloader source?
When bootloader mode is first executed using fds, specific data stored in fds is detected and if the condition is true, we tried to implement the function to proceed with DFU, but it could not be implemented due to an error.
Do you have an Area restriction for Bootloader Area?