The “Import Movies” step of the tutorial explains…
Select the Gain reference path with the file browser: Select the single .mrc file in the folder where the test data was downloaded.
However, the command cryosparcm downloadtest now downloads a dataset empiar_10025_subset_v1.tar that contains more than one mrc file. Perhaps update the tutorial to explain which mrc file is the gain reference, and update tar -xf empiar_10025_subset.tar to tar -xf empiar_10025_subset_v1.tar