Pimoroni contacted me and lead me to the solution to the problem. So, I hope this might be useful to others who stumble upon this thread. In the config.txt file insert the line:
display_rotate=0x1000
That fixed me problem of a horizontally flipped display.
If someone else has a slightly different issue, here is something from a different website that talks about different ways to rotate/flip display (I am not sure about the difference with the “hdmi” in the command :
Use display_hdmi_rotate to rotate or flip the HDMI display orientation. The default value is 0.
display_hdmi_rotate
result
0 - no rotation
1 - rotate 90 degrees clockwise
2 - rotate 180 degrees clockwise
3 - rotate 270 degrees clockwise
0x10000 horizontal flip
0x20000 vertical flip