sparkfun nRF52832 Hook-Up Manual page 12

You should see the red power LED illuminate. If it doesn't power up, make sure you haven't disabled
the FTDI-VCC EN jumper on the back of the board.
Triggering the Bootloader
Unfortunately, the nRF52832 Breakout's bootloader doesn't feature an auto-reset function like many
Arduino's. To decide whether to enter the bootloader or run its application code, the nRF52832
samples the state of GPIO 6 when it boots up. If pin 6 is LOW, it enters the bootloader, otherwise it
boots into its programmed application
So, to boot the nRF52832 into its bootloader you must reset the chip while holding down the pin
6 button. In step-by-step form, the trick to resetting into the bootloader is:
1. Press down on both the RESET and 06 buttons.
2. Release reset.
3. Verify that the blue (pin 7) LED begins blinking.
4. Release the 06-labeled user button.
While in bootloader mode, the nRF52832's blue LED on pin 7 should blink at increasing speed in
what we call the "timebomb" sequence.