There are two tilemap expressions TileToPosition and PositionToTile with that you should do what you want. For example change Tile on a positionXY:
Sprite| Is overlapping Tilemap -> Tilemap| set Tile(Tilemap.PositionToTileX(Sprite.X),Tilemap.PositionToTileY(Sprite.Y) to tile 1
Create object on a tile number 10 in x and tile number 10 in y.
event -> System| Create object Sprite (Tilemap.TileToPositionX(10),Tilemap.TileToPositionY(10))