You have to look at it's under there...
Typically males have two simular sized holes oo
females have one that is bigger oO
The bigger one being the egg tube inverted while not in use.
Easiest non invasive way to do this is if you are able to get the fish near vertical close to the glass to grab a picture or three. Then you can use your editing to zoom in and see what you have.
My Oscar loved freeze dried krill. She knew the bottle it came from and would wait impatiently for her treat. So I was able to get some pic's and find out she was a female.
Here she is waiting for her treats
And after zooming in in editing you can clearly see that's she is female.