How do I perform fatalities with "up" commands?

Current Fighting Games Mortal Kombat
1

How do I perform fatalities with “up” commands?
I have tried executing the move as listed and while holding block another time. I can’t figure it out. I can’t stop my character from jumping.

2

Hold block while inputting the directions, then let go of block and hit the corresponding face button. Otherwise, jump, and then input the directions while you’re landing, although I’ve seen very limited success with the latter method.

3

Thanks Skudd I must have done something off