How to access selected tiles in a macro ?

I use tiles to display my players' characters and npcs on a background, but when I drop an image (using the Drag Upload module), they often are way to big, and I have to manually resize them. I would like to create a macro that reduces the size of the tiles I am selecting, but I can't find how, as it doesn't seem to work via user.targets. Is there a way to do it ?

Thank you

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Edit : I have found that using this allows me to selected multiple tiles and iterate on them.

canvas.tiles.controlled.forEach(i => {
    console.log(i)
})

Now I'm searching how I can change their size, as modifying their width or height doesn't change the image size, only the tile's.