Gender classification using Periocular Region
You can't if you have nothing to start labelling them with. 

As you describe it, there's simply no info available (not even about statistics) about the gender of your reference images, so there's nothing you can train.

What you can do is use a different technique (as you say "biometrics say..." I assume there's a non-ML method of classification) and run it over the dataset, and use the resulting labels to train your neural network. Discussion of the sensibility of that is left to you as an exercise for your report!