I am still waiting for the UART connector to be delivered and in the meantime I opened the box which was actually quite an effort. 
I was somehow expecting to see a UART socket on the board, but could only find 4 pin holes at the edge so far.
Maybe it is located underneath the heatspreader, but I am hesitating to remove it.
Is it plausible that the pin holes are connected to the UART transmitter like mentioned in Using UART with ‘holes only’?
If yes, how am I able to determine the correct mapping of Rx, Tx and Gnd?
Trial and error?