You can get a Pickaxe as a reward in the Evets. Also, you can purchase it in a package from the Bank.
Pickaxes are placed in the bottom right corner of the level game screen. If you click on the plus sign under the Pickaxe you’ll be able to buy new ones.
With the Pickaxe, you can collect any tile you want without spending a move. To use it, just click on it and tap on the tile you want to remove.