@Peter Grainge please help to sort the issue
Sorry but this is a user to user forum, not a 24 hour paid support site. Your first post was at 05.45 my time, your chaser was at 06.42 my time and you added to another thread at 07.38 my time. I'm sorry but I have this nasty habit of sleeping at night. I tried to kick it when I was younger but the price was too high so nowadays I sleep at night.
Your problem is not the same as in the other thread where you have posted. In your case you have not understood the difference between the start page and the default topic. The start page is what opens the whole help, the default topic is the topic that appears within the help. There are separate fields for each in the dialog where you configure the output.
AIR Help does not have a CHM file so you need to clarify that.
As this seems to be your first foray into AIR help I think it is worth emphasising that this is a form of help that did not really take off and Adobe have not fixed any bugs in it for several releases of RoboHelp. I think you would be better off looking at WebHelp or one of the new Responsive HTML5 layouts for anything web based. If local then generate WebHelp and then convert it to a CHM. How is described in the RoboHelp Tour on my site.
Now I'm off to breakfast. If you have any follow up questions that's fine but give me a chance to respond.
See www.grainge.org for RoboHelp and Authoring tips