If you put the filepath into a variable, you can refer to the variable as the source file for the import. The trick is to keep two file references like this in your Import Records script step:
Where "SampleFileName" is a direct reference to a specific file by name.
The second reference makes it possible to specify the field mapping and other import details when you set up your script, but the script will assign a value to $Pathvariable so it will identify the actual file used as the source during import when you run the script. (I really tore my hair out one evening until I chanced upon this trick by accident.)