The function will return you the result (Accuracy,Recall,Precision,F1,F2,F0.5) based on your input (Actual and Prediction).

For example,

load fisheriris
X = meas;
Y = species;
Mdl = fitcknn(X,Y,'NumNeighbors',5,'Standardize',1);
predictedY = resubPredict(Mdl);
[table_ind_result,table_ove_result] = summary_confusion(Y,predictedY);