cant upload a sketch on adafruit nrf52832 | i need help

hi first time using this adafruit. error keeps appearing cant upload a new sketch. already installed adafruit drivers. and correct board in board manager. i also tried grounding dfu pin nothing happens, need your help im very new to this,

Upgrading target on COM3 with DFU package C:\Users\axL\AppData\Local\Temp\arduino_build_392042\sketch_feb26a.ino.zip. Flow control is disabled, Single bank, Touch disabled
Timed out waiting for acknowledgement from device.

Failed to upgrade target. Error is: Attempting to use a port that is not open
Traceback (most recent call last):
  File "nordicsemi\__main__.py", line 294, in serial
  File "nordicsemi\dfu\dfu.py", line 235, in dfu_send_images
  File "nordicsemi\dfu\dfu.py", line 206, in _dfu_send_image
  File "nordicsemi\dfu\dfu_transport_serial.py", line 213, in send_firmware
  File "nordicsemi\dfu\dfu_transport_serial.py", line 241, in send_packet
  File "site-packages\serial\serialwin32.py", line 304, in write
serial.serialutil.SerialException: Attempting to use a port that is not open

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.

this is solved. solution is burn new bootloader.. follow the tutorial on adafruit page