How can I activate the UART Ports on CON3

Hello, I’m running a BananaPi Pro A20 Dual Core Board. I need to activate one of the UART Ports on CON3. Problem is, that I’m also running a SSD Drive so that I do not get access to the SD Card anymore. Therefore I did not get along with all the decriptions using the Terminal Interface AMA0.

All trials to get access by configuring the software using the serial interface were not successful.

Any suggestions? Regards Norbert