Getting access to your Mikrotik Router via serial cable is rather easy. I’m using picocom but everything should work with minicom or similar program as well.
Assuming the serial console cable from your Laptop to the Mikrotik device is located at /dev/ttyUSB0, I could connect to my Mikrotik device using
picocom -b 115200 -r -l /dev/ttyUSB0
(optional) Configuring the device
It might be necessary to first hand configure the Mikrotik device itself
/port set serial0 baud-rate=19200 data-bits=8 parity=none stop-bits=1
You can also try to let RouterOS guess the needed baud rate by setting
/port set serial0 baud-rate=auto