You probably need to wait a while and the option will come back. In my opinion air mode is pointless, just set it to 21% Nitrox.
You say you set a SECONDARY gas to 32%. Did you then select that gas on the dive? Are you sure the computer thought you were actually using 32%? Were you diving 32 or was that your buddy?
The treatment of which gas is considered on a dive is slightly complicated.
There are the gasses you are carrying and expect to use and want considered for your ascent timing, then there are the gases someone else is carrying and you might want to switch to if you borrow them. Last 5here are gases you left at home but don’t want to be reentering when you actually use them.
There needs to be a way to tell the computer that. My Suuntos are all lent out and of the generation before the DX but I seem to recall that Primary means “I have it and plan to use it”, Secondary “it is here somewhere but not the plan, I may need to switch to it but ignore it for TTS” and off means it is in the garage at home.
If you are personally diving the 32 you probably just want one gas programmed as a primary and change that between 21 and 32 dive by dive. Then there is no question about which gas is being used. For no stop dives where you and your buddy are on different gases then the different mixes are the least of your problem in an air sharing situation and telling the computer you are on a different mix is likely to be counterproductive.