To save an option combo so you can trade it again later (even after you have closed your position) you must add it to a Watchlist. Once you have created your option combo in IBKR Mobile using the Strategy Builder within Option Chain & Combo Builder, click the "+ Watchlist" button. If using the Spread Template screen, click the "+Watchlist" button at the bottom of the screen. A window will populate asking if you want to "Add Individual Legs", "Add Strategy" or "Add Strategy and Individual Legs". Select your desired option and tap "Done". On the next screen, select the Watchlist you wish to add it to by tapping on the Watchlist name followed by "Add". The combo strategy will now be added as a line item to your Watchlist so you can monitor the strategy's bid/ask and use it to create new orders.
Find more information on the Strategy Builder for IBKR Mobile for Android and IBKR Mobile for iPhone in the User's Guide.