I don't think this is how you're supposed to do it but you can throw the magnet through the little hole when the big block in the middle is up
As for feedback on the game, the general concept and feel of the game is great, the puzzles have a lot of potential and are generally executed well.
However there are multiple levels where it is easy to get stuck, in the level above alone I've had moments where I've fallen of while the door is as you see in the picture which means a reset, I fell in the hole the box is in, a reset, I've lost my magnet next to the switch and fallen down, another reset.
A possible solution to this is making the player able to call the magnet to them, though this might not work well or require to much redesigning.
Another solution is to simply make it harder to get to areas without the magnet if you're supposed to have it with you, though I'm not sure on how you'd implement that.