When this happens you can select any tile and you flip the tile over (becomes a gardner) and you can place it anywhere.
I think this is mixing up two things.
You may select any tile in this instance, but you must place that tile in the column marked by the symbol on that tile, and in the row marked by the color corresponding to the colour of the game board space where you got that tile from.
You only flip a tile over (i.e. becomes a Gardener) if the square where you must place that tile is already occupied. Even then you can't place that Gardener wherever you wish - it must go in either the same row or column as the occupied square.