I found this online

Code:
In the Adafruit_SSD1306.h file look for the lines:

#define SSD1306_COMSCANINC 0xC0
#define SSD1306_COMSCANDEC 0xC8

Change these lines to say:

#define SSD1306_COMSCANINC 0xC8
#define SSD1306_COMSCANDEC 0xC0
this supposed to flip the image on the y-Axis.

but i'm not so experienced to know where in the teensy GC9A01A library code to set these

@mjs513 likely to help?

EDIT: My bad, that's for a different library!