No special conditions are required.
1. Sodium sulfite has obvious reducibility and is easily oxidized when it encounters an oxidizing agent.
2. Oxygen in the air can oxidize sodium sulfite:
3. Other unknown oxidants in the air may also oxidize sulfite.
If you have to say the conditions, it is exposed to the air.
The rate of oxidation is not too fast.
The condition in which sulfur dioxide is oxidized by oxygen in the air is to contact a catalytic substance such as drifting dust.