My grandson has been constipated for a few days now, what can i do?

Need more info: I'm assuming based on your age being a grandfather, that he is a small child or infant. Formula feeding can be constipating, though breastfed infants can get that way too. If he's comfortable it will "pass" so to speak. A bit of pear or apple juice can help. A rectal temperature, giving rectal stim, can induce pooping. Anything else required, contact his pediatrician for further guidance.

Diet modification: For immediate relief you can try using a glycerine suppository, or give him miralax (polyethylene glycol). Over the long run he needs to have his diet modified by reducing the milk and milk products he eats, increase the fiber in his diet by giving him fruits and vegetable, high fiber cereals and replace white bread with whole wheat bread. No apple or pear juice since they contain pectin and can be constipating.