I am wanting to replace the value in one row with the value from a different row based on a certain condition.

For example, I want to replace the value 48,728 in the Total RSF column with the value 45,196 from the Project RSF column. So the formula would look something like if Tenure equals "Leased" and Project RSF is Null(), then I want to take the value in Project RSF and replace the value in Total RSF with it.
There are another 50 cities to do this for, which may have more or fewer records (if any records at all) and their figures will be different. Does anyone have any ideas on how I can accomplish this?
Edit: @vizAlter I created a sample file and attached it. What I want to do is if the Project RSF is Null() and the Tenure equals "Leased," then put the Project RSF value from the other row in the Null position.

So the blank area where the red box is, is where the Project RSF needs to be added.