When 52840-DK compiles with MbedIDE, it will generate the message in the lower left corner of the screen. The DapLink pre-program is installed. If you drag the compilation file to DAP_Link hard disk, it can be burned. Trouble experienced people to help ans
There is some support for the nRF52840 DK in mbed, but I don't know how mature it is. I recommend you ask in the mbed forums instead as the mbed port is done by ARM and not by Nordic.
