In inference view, click on 
within "Result"
A dialog will appear for you to create or choose output directory. Choose or create a new directory to host the output membership maps, click on "Ok" , the selected directory will appear on the "Save membership files to folder " text box.
Click on "Execute" to start the inference process.
If inference is completed without error, in the result folder you can see the similarity file for each soil type you specified.