The expression for a truth table of all false is: F
The expression you can add to handle false rows is F, which gives the desired output for the target row and false for all other rows, just like the expressions you construct for true rows.
Having “or F” one or more times is unnecessary but harmless and makes it easier to see how a truth table with all F outputs works: you get: F or F or F or F which you can simplify to just F. (F or F = F)
make sense?