Pro Mini nRF52840 set up issue

I set up the board using the hookup guide and arduino development guide. I loaded the board manager and definitions as instructed. I installed the nrfutil via cmd line and blue LED 7 is flashing to indicate DFU mode. I’m trying to upload the example sketch (latest version from github) and am receiving the following error messages:

Library Adafruit_nRFCrypto has been declared precompiled:
Using precompiled library in C:\Users\cstep\AppData\Local\Arduino15\packages\adafruit\hardware\nrf52\1.1.0\libraries\Adafruit_nRFCrypto\src\cortex-m4\fpv4-sp-d16-hard
Sketch uses 91804 bytes (11%) of program storage space. Maximum is 815104 bytes.
Global variables use 13972 bytes (5%) of dynamic memory, leaving 234860 bytes for local variables. Maximum is 248832 bytes.
Upgrading target on COM3 with DFU package C:\Users\cstep\AppData\Local\Temp\arduino_build_610844\blinky_ota.ino.zip. Flow control is disabled, Single bank, Touch disabled
Timed out waiting for acknowledgement from device.

Failed to upgrade target. Error is: No data received on serial port. Not able to proceed.
Traceback (most recent call last):
  File "__main__.py", line 296, in serial
  File "dfu\dfu.py", line 235, in dfu_send_images
  File "dfu\dfu.py", line 199, in _dfu_send_image
  File "dfu\dfu_transport_serial.py", line 179, in send_start_dfu
  File "dfu\dfu_transport_serial.py", line 243, in send_packet
  File "dfu\dfu_transport_serial.py", line 282, in get_ack_nr
nordicsemi.exceptions.NordicSemiException: No data received on serial port. Not able to proceed.

Possible causes:
- Selected Bootloader version does not match the one on Bluefruit device.
    Please upgrade the Bootloader or select correct version in Tools->Bootloader.
- Baud rate must be 115200, Flow control must be off.
- Target is not in DFU mode. Ground DFU pin and RESET and release both to enter DFU mode.

help? I really don’t want to flash a new bootloader. how can I change the selected bootloader version?