Hi. Yeah, imaginative username I know., don't hold it against me.
SO - I downloaded Welder from the iTunes app store for my Mac and am just getting to use the game - I'm only up to Level 3.
Apparently some tiles can only be swapped with "the wrench". The problem is - I don't see no wrench. The alert shows a little wrench icon - alas, there is no such icon on my screen.

So what's the trick? How do I activate the thing? It's going to get tiresome really fast having to work around these wrench-lovin' tiles.

There is a wrench button in the HUD at the bottom of the screen. However, I think what is happening is that you have triggered a dialog box that reminds you about the wrench (because there are a lot of empty spaces on the board), but you have not passed Level 4 for the first time and the wrench button is dimmed out. (That is on a bug fix list!).

If this is the case complete Level 4 and the wrench will become un-dimmed.

However if you are above Level 4 or have passed Level 4 before, the wrench button has a little wrench icon on it at the bottom of the screen.

thanks for playing!