We'll add a set of header sockets to Matrix Portal in order to easily plug in the servo motor. A 90º header makes for a nice, compact-yet-accessible setup.
There are eleven GPIO pins exposed on the Matrix Portal's header row. Trim a section of socket headers to fit as shown.
Place the header and solder it in place.
Use small pliers or diagonal cutters to cut off a three-pin section of extra-long header pins and use them to insert the servo motor connector as shown here