For everyone who is struggeling I followed these instructions:

-Download the STM32 ST-LINK Utility tool and try to connect to the board.

STM32 ST-LINK Utility:

www.st.com/.../stsw-link004.html

-If the Utility tool fails to connect with the board try tying your boot0 pin high, resetting the board, and reconnecting. On my board this meant using one of the extra jumpers from CN11/12 and connecting pins 7 (boot0) and 5 (VDD) together. Your board's User Manual will tell you where the boot0 pin is and might also tell you how to tie it high. Ofcourse you need to select correct port (in my case it was 3 because I tried to connect to M4 core).

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