You can create a new Freeholder, RTM, or Company (if they are not already existing) by navigating to 'Creation Center' .
Once you have the Freeholder/RTM/Company on the system you can now open the block you need to change over and navigate to 'Block' > 'Block Details' and you can choose the management structure here.
If you can't find your Freeholder on the drop down box it might be that they need assigning to this client or block. To do this simply find and open them under 'Settings' > 'Agency Contacts' > 'Users'. Now you can check that the client and property is ticked under the 'Client Access' and 'Properties' tabs respectively. If they are not assigned then simply tick the correct client and property and click 'Update'.