EM-ELM Cross validation
Cross-validation can be used to tune any hyperparameter.
One way tune Extreme learning machines (ELM) with cross-validation is to:

Fit a model to a subset of the training dataset. Measure performance on a validation dataset with a evaluation metrics.
Change the number of neurons hyperparameter.
Fit the updated model to a subset of the training dataset. Measure performance on a validation dataset with a evaluation metrics.
Compare the two models and see which model is better on a evaluation metric on their respective validation dataset.
Repeat steps 3-4 until satisfied.