Do you want to write-down the value of assets you have in AssetAccountant™ to zero, but not actually write them off, or dispose of them?
Because by doing those things would remove them from the register and not appear in your asset reporting.
Further, you have not actually removed the assets from use, nor disposed of them because the assets are still on-hand.
The AssetAccountant™ functionality you require to achieve this is a Reassessment to change the depreciation method to IMMEDIATE at the date you require.
This will have the effect of leaving the asset in use, but leave a written-down-value (net book value, WDV) of $0.
See this video: Reassessments
Don't forget to reassess for both tax AND accounts (if applicable).