This should work:
+System: On start of Layout
+System: For "x" from 0 to Tilemap.Width/32
+System: For "y" from 0 to Tilemap.Height/32
+Tilemap: Tile (loopindex("x"), loopindex("y")) = 1 -> Tilemap: Set tile (loopindex("x"), loopindex("y")) to tile choose(1,1,1,1,1,1,1,1,1,2)
Edit: "32" = size of your Tile - 32x32 in this case