To add a landlord float, please go into the landlords account first > actions > adjust float:
Here you will what the current float balance is and what the minimum balance is set to (if there is one in place).
If you want to change the custom float amount that is in place just pop the amount in the field.
You also have the option to do a manual float refund to bring money temporarily out of the float account. The account will then be topped up to the custom float amount when more credit comes into the landlords main account.
There is generally no reason for a journal to be made in or out of the float account as the above actions should action what it is you're trying to do. But if you do feel the need to action a journal, please feel free to contact the support team.