When you install the new inmusic version of BFD3 it creates new folders that (I think) are almost identical to the old fxpansion ones but they are just in the new BFD Dums folders, so where you have an fxpansion folder in your documents in which your grooves/kits/maps/presets/ and other folders are, you will now have a BFD Drums folder in your documents, inside of which are the same folders. So you can manually move your kits/presets/maps form the fxpansion folders into the new BFD Drums folders of the same name.
During the migration process, an inMusic account will be created for you automatically using the email address assigned to your fxpansion.com account. If you no longer have access to this email account, you will need to change this in order to complete the migration process.