The creation and customization of database applications using Microsoft Access
You can do this in the query or in the report. I would use the expression:
IIf([AnotherFieldNameHere], [FieldName], "unavailable")
This would mean if [AnotherFieldNameHere] is true, display the contents of [FieldName]. If it is false, display "unavailable".
This could be a new column in a query or in a text box control source following an equal sign:
=IIf([AnotherFieldNameHere], [FieldName], "unavailable")
The name of the text box control in your report can't have the same name as a field in the report's record source if your use the "=..."