How do I pick the app orders out of my orders export?

By the Notes column. In the orders CSV from the orders board, an app order carries the app's name and the app's own order code in Notes, so a filter on that column finds them. On the board itself the line names the app. Their money is in the totals like any other order, because the total we record is the total the app told us. The Orders from delivery apps tab in the docs covers reports and the export.