There is a new version of the SODAQ SAMD boards for Arduino’s Boards Manager. It’s version 1.6.5. (Notice that the SODAQ AVR boards are still at version 1.0.3)
New in 1.6.5 is an extra “board” called “SODAQ Autonomo with Serial2”. With that board selection you can connect a serial line to D6/D7. D6 is RX, D7 is TX.
As an extra reminder, you should have this url in your Arduino IDE preferences, and if you don’t, you should.