KNN Matlab Train Test Cross-validation

So I want to use my the data that I defined below (has two labels) and use KNN for training and testing and also cross-validation. I could not find matlab tutorials useful so I appreciate it if you guys can help me. Imageine I have Data=rand(2000,2); Lables=[ones(1000,1);-1*ones(1000,1)];

I want to use KNN and have: 50% of the data for training. 25% cross-validation 25% testing

Thanks in advance.