how can i change tile map collider2D's outline collider to shape?

(sorry for bad english) i was making a water in tile based 2D platformer game, but tile map collider gives me just outline collider. which can not fit with water.(water is passable, so character can go inside of water tile. )

how can i fill inside of that outline coliider? I googled for three days but couldn't find an answer. (Composite collider2D's geometry type: outline->polygon doen't help me at all. i think i need to do something with tilemap collider2D)