How can I delete all tiles from a tilemap instance when starting a new level design?

How can I delete all previous tiles from a new tilemap instance when starting a new level design?

Select a large area of tiles, then switch to eraser tool and you will be able to erase this area. Once you clear the entire tilemap, make several copies of it on an unused layout. Next time when you need an empty tilemap to design a new level - you will have spares.

Thanks! Didn't realize that the tile selection affects the eraser size!