inverting screen on sparkfun flexible oled

Hi, this is the start of my journey into Arduino programming, i have spent a long time trying to get to grips but have come to a halt trying to invert the black and white on my oled display,
the code is below, any help will be much appreciated

/*
Control a SSD1320 based flexible OLED display
By: Nathan Seidle
SparkFun Electronics
Date: November 21st, 2017
License: This code is public domain but you buy me a beer if you use this and we meet someday (Beerware license).

Basic ‘hello world’ example.

To connect the display to an Arduino:
(Arduino pin) = (Display pin)
Pin 13 = SCLK on display carrier
11 = SDIN
10 = !CS
9 = !RES

The display is 160 pixels long and 32 pixels wide
Each 4-bit nibble is the 4-bit grayscale for that pixel
Therefore each byte of data written to the display paints two sequential pixels
Loops that write to the display should be 80 iterations wide and 32 iterations tall
*/

#include <SSD1320_OLED.h>

//Initialize the display with the follow pin connections
SSD1320 flexibleOLED(10, 9); //10 = CS, 9 = RES

void setup()
{
Serial.begin(115200);

flexibleOLED.begin(160, 32); //Display is 160 wide, 32 high

flexibleOLED.clearDisplay(); //Clear display and buffer

flexibleOLED.setFontType(1); //Large font
flexibleOLED.setCursor(28, 12);
flexibleOLED.print(“Hello World!”);

flexibleOLED.setFontType(0); //Small font
flexibleOLED.setCursor(52, 0);
flexibleOLED.print(“8:45:03 AM”);
flexibleOLED.rect(2, 2, 40, 12); //X, Y, Width, Height
flexibleOLED.rectFill(2, 2, 40, 12);
flexibleOLED.circle(15, 20, 10);
flexibleOLED.circleFill(150, 15, 10);
flexibleOLED.display();
void setContrast(uint8_t contrast);
flexibleOLED.setContrast(100);
void invert(boolean inv);
flexibleOLED.inv(invert display);

}

void loop()
{

}