[CE] PCF UPGRADE

I'm trying to follow the steps shown in the help document regarding upgrading existing PCF files:

https://docs.bentley.com/LiveContent/web/OpenBuildings%20Designer%20Help-v4/en/GUID-9B0F78CB-DEFE-41E7-BC3A-4E7B47D3F381.html

And I just couldn't understand the instructions:

Projects created in previous editions of OpenBuildings Designer need to be upgraded to WorkSets. Use the following steps to upgrade a set of .pcf files to WorkSets (.cfg) using key-in:

  1. Open the WorkSpace into which you want the WorkSets to be created. If you do not have a WorkSpace, create a new one.What does "Open the Workspace" means? Select the workspace in OBD? Open the workspace folder in Windows Explorer? 
  2. Redirect the WorkSpace's WorkSpace location to the folder that holds your .pcf files. You can do this by setting _USTN_WORKSETSROOT configuration variable.Again, what exactly does this mean? Which cfg file should I use to set _USTN_WORKSETSROOT new value? 
  3. Open any DGN file in that WorkSpace. Any workset will do? 

Best regards,

Tuan Le