In its most simple type SVM is applied on binary classification, dividing data points either in 1 or 0. your case is a multiclass classification, for which, the same principle is utilized. The multiclass problem is broken down into multiple binary classification cases, which is also called one-vs-one. for instance, in Python, scikit-learn one-vs-one is not the default case and needs to be selected explicitly using the parameters. One-vs-rest is set as default. It basically divides the data points in class x and rest. Consecutively a certain class is distinguished from all other classes.
Please take a look at, https://www.kaggle.com/pranathichunduru/svm-for-multiclass-classification
You can set a threshold. If the classification result is over the threshold, you can think it is right. Additionally, you can use cross-validation method to test the accuracy of classification reslut.