Use the .op2/.odb file field to specify the full path and filename of the results file containing the desired GPFORCE output for the current model.

Clicking on the folder icon opens the standard file selection dialog window for browsing files.

When a results file is selected, loadstep names and IDs with GPFORCE output are saved to the database for use with all FBD utilities.  The loadstep name and ID information is retained within the database once saved.  If a new results file is required, or if the original results file changes, you must load the new results file into the database, overwriting the previously selected.