InfoPath Dev

I am trying to get a form to connect to a Sp library, find the max PONo from my forms in the library update that POno and use the new

PONo On my new form and as part of the file name.  I've got it  coded but not working.  I am a Junior level developer.  Can someone help?

You don't need code to do this. Just use xpath to get the count of the ShP list and use concat to add it to your filename on submit.