Freezerworks will require a unique identifier to be included in the import in order to select which aliquots you are updating.
Freezerworks will accept:
The Unique Aliquot ID (system generated unique number for each aliquot)
A unique User Defined Field (must have the unique property selected in Field Configuration)
Aliquot Number combined with a unique sample level field.
Once you have added your fields on the Import Fields tab, go to the Import Settings tab and select the Import Type of Modify.