Good day. my three week old has green slimy poo. should i be concern or is this normal? what can i do?

Likely okay: In early infancy, especially breast fed infants can have quite loose/watery poop that will flow easily out of a loose diaper. Formula feeding has more residual bulk & is commonly firmer. The color greed comes from the green bile added in transit that has not had time to change through yellows/browns. If the kid wets every 6 hrs & is otherwise comfortable it is normal.