Depends on what species, without knowing what they are isn't a great option.
There are a few things that may or may not work.
Many males have eggs spots on the anal fin, while females don't, the egg spot enduce the females to try to pick them up, allowing the male to get sperm to the eggs in the females mouth.
Another trait is some males are more colorful, and with some species the males are a different color than females.
Here is a male Nimbochromis livingstoni, note the yellow on the anal fin, that resembles yellow eggs

Now an immature male, this is the color females keep, but you can also see the egg spots better in this shot