Welcome!
First, the stringApp definitely works with 3.7.1. The app requires a *minimum* of 3.6 for all of its features to work, but can work with any future 3.x.x version.
Now, to use the stringApp, you can simply perform your query in Cytoscape. You don't have to perform it at STRING website and them save/import a txt file. The point of the app is to avoid those tedious steps :)
Here are tutorials on how to use the app:
- Alex