How to apply knn classifier with k-fold cross validation.

Hi. I have an HW but instructor wants us to solve it with MATLAB. However I am an R guy. So I am going to need your help a little.

The question wants us to use PCA on a data set which is done. Then it says;

_ Which one of these two PCA approaches are feasible for a real problem? Answer by considering how you would classify a new instance using the projections you obtained in a) and b) and using KNN5 classifier. The KNN5 (5 nearest neighbor classifier) labels a data point x as follows: Find the nearest (in terms of Euclidean distance) 5 points to x from the training set, label x as the majority of its 5 nearest neighbors’ label. (You should evaluate classification results using 10 fold cross validation)_

I have my two PCA results and I don't know how to apply knn5 on them with 10-fold cv. Can anyone tell me how to do it? Thanks in advance.