nrf52832-dk + DFU over BLE + External flash using W25Q64JV

We are trying to make DFU over BLE with external flash to overcome the large application size.

Environment:
->nrf52832
- >nRF Connect SDK (v1.8.0)
- >External flash (W25Q64JV) connected over SPI and tested successfully

Could you share some sample or guide which shows OTA using BLE with external flash?

 we need to do the following changes:
- Modify our application for DFU over Bluetooth
- Add a new file in our application folder pm_static.yaml and modify it.
- Add new child_image/mcuboot/prj.conf in our application. (Not sure if this is required)
- Is there any other configuration required in our application overlay file?

but we are not succeed  is it possible to use ble dfu on nrf52832-dk using external  spi flash ?    
or any way , we can achieve DFU BLE innrf52832 using external flash w25q64jv  ?

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