Room editor: shift all instances by x amount

Pretty sure this was possible in GM 1.4, but haven't found out how to do this in GMS 2024.2+ (Windows).

I increased the width of a room by x pixels, which added that amount in empty space to the right of the existing content. Since I want new content to be to the left of the existing content, I want to shift the existing content right (all by that x amount) to fill in the new space.

The best option would be a simple input to shift all existing tiles. If that's not available, I can try...

Room editor: shift all instances by x amount