Here is the ATO Rules:
https://www.ato.gov.au/general/capital-gains-tax/shares,-units-and-similar-investments/investments-in-a-company-in-liquidation-or-administration/
Prior to any declaration by administrator/liquidator, to declare a loss you would need to make an actual arms-length disposal.
Delisted.com.au will do it for you, but it costs.