Here's your answer: https://www.scirra.com/store/games-with-source/sokobanboxman-puzzle-game-3801
People are trying to make money out of their invention "how to use Construct 2 to make a sokoban clone"
I've been doing the same thing you've done, but I prefer to figure it out myself.
So far it appears that sokoban is so simple that Construct 2 is too powerful for it.
None of the OOTB plugins (Physics, Platformer, Solid, etc.) are useful in making a Sokoban clone. At least I couldn't do it properly with them. So all you have to think of is your size of the "grid" and how much your player sprite should move on X and Y when you push the respective button.
I hope that gives you some insight.
P.S.: I recommend you try RPGMaker as I was able to make a sokoban clone there in less than a week.