Each building's operating account defaults to the account of the owning company.
Viewing Default Operating Accounts
Navigate to the Properties page, and select any unit from the desired property.
Go to the Property tab, and scroll down to the Operating Accounts section to see the current operating account.
Changing a Building's Operating Account
Under the Property tab > Operating Accounts section, hover over the Operating Account until you see the pencil icon
Click anywhere in the greyed-area to enter edit mode (see Editing Fields article for more information).
Select the desired operating account, and click Save at the bottom-right corner to confirm your changes
For more detailed guidance, refer to Separate Books by Company/Setting Operating Accounts.