Important Note: Be sure that File Settings are not being saved on exit either through Preferences or some other manner. If Settings are saved when closing the file will be reassociated.
1) Open the file (will open with the wrong WorkSet associated to it). Once the file opens you can verified in properties dialog what WorkSet was used. See image
2) With file opened, run the Keyin: File Disassociateworkset
This will break the association with that WorkSet (MetroStation in this example). See image
3) Close MicroStation CONNECT and open the file again, this time select the correct Workspace\WorkSet or the No Workspace\No WorkSet if none is used. See imagen