Block form change help! (a mom's request)

Hello all, 

My 11 year old is pretty familiar with Mcreator and often happily textures away at lava and trees and what have you. Recently, however, he has started making more complicated things happening and last night we had a bit of a crisis occur. 

He was trying to make some of his falling blocks (naturally, from an explosion of some kind) change from one block type into another block when they reached sea level. Well he couldn't figure out how to do it on the triggers page or whatever that page is in Mcreator. Now, dr google is very happy to tell me in text form that the logic will support this type of thing and even give me a version of the logic, something like: 

if [y coordinate] <= 63
AND [block at x y z] = MagmaBlock
Then:... or if [y <= 63] AND [block below is water]

BUT I don't know HOW to actually use Mcreator... and this is actually where my son got stuck and why he had a bit of a meltdown. He doesn't know which of the blue boxes to use and how to fill in the fields to make the trigger. 

Would anyone be willing to help us out? Pretty please? Maybe you have something similar and could share a screenshot or at least tell me which of the little blue boxes to be using and in which order to put them? I promise to send you the strongest positive cosmic karma vibes I possibly can :) 

I appreciate your time!

Thank you.