How to create an ROC model using three classes

I am trying to create a ROC plot based on response variable with three classes. I believe that is possible based on the answer to this question Here. In the answer provide in this question though, they are getting the pred using NaiveBayes to get the model, but I’ve already created my model and predictions. Does anyone know how I can apply the code to create a ROC for my model and my predictions?

Just to clarify:
I see in the code that he does Naive Bayes for each class. I created my model different for the three classes using rpart() then pruning based on the calculation for the best CP. I’m worried that I have create a model for three of the classes using a naive bayes. It’s not really going to give me an ROC chart based on the model that I created previously. I guess my question is would the ROC created in the way I linked actually reflect the model I created previously.
If it won’t reflect model, which I believe that it won’t, is there way for me to do a similar thing done in the question I linked using the model I created in rpart? I hope this clarifies my question a bit more.