In addition to the code you used you have to add setters in Java class for all fields you present in inputboxes for change, e.g.
public void setApplicationTitle(String applicationTitle) {
this.applicationTitle = applicationTitle;
}
and add a method save()
public void save() throws NotesException {
Database db = ExtLibUtil.getCurrentSession().getCurrentDatabase();
View view = db.getView("config");
Document doc = view.getFirstDocument();
doc.replaceItemValue("ApplicationTitle", applicationTitle);
doc.save(true, true);
doc.recycle();
view.recycle();
}
and call this method in a button using SSJS
#{javascript:config.save()}
This is just a starting point for development. In addition, you have to care about possible exceptions. You should also allow changes for admins only as this config document seems to keep general settings for your application.