It’s likely that the human faeces turned into sludge are smelly because they were composted anaerobically (low oxygen) and/or mixed with urine.
This smell will quickly disappear if the sludge is mixed with enough dry carbon-rich material (dried grass clippings, sawdust, wood shavings, coconut fibre - coir) to fluff up the sludge as it is added to in the Subpod composting environment.
Using aromatic wood shavings can help.
Alternatively, mixing the sludge with crushed charcoal (raw biochar) as you add it to the Subpod, will be the most rapid way to stop the odour.
The aeration panel that is built into the Subpod will help to keep the Subpod aerated and anaerobic (less smelly) also.
When you add anything to Subpod, make sure to use the compost aerator to mix in the waste evenly throughout the system, whilst also mixing oxygen through the compost.
Please remember that you should use a separate Subpod for any faeces that you are composting. Only use this Subpod for plants that are not for human consumption.