If it's available, you would see it in your reservation in aa.com or on the AA app. But,I've never seen upgrade offers on award bookings though I see them with every single cash booking. The offer is dynamic and could change from one day to the next, up or down. Likely an algorithm constantly adjusting the offer based on loads and other data we're not privy to. AA doesn't have any upgrade bidding.
You may have to pull down to refresh a few times to see the offer, the app can be finicky about that.