When a coach calls a player about his "attitude"...I notice if the player gives a positive response...his relationship with his coach improves.

If a player has a poor/decreasing attitude with his teammates...what can a coach do/attempt to help turn that situation around?

When you call a player about attitude, sometimes his relationship with the coach improves, other times it doesn't change, and other times it goes downhill.

Not much you can do with regard to his relationship with other players, other than calling him to let him know you've "heard he's having difficulties with some of the guys". Over time, sometimes the relationship will improve, other times not. Of course, if his "personality" is lousy, it's going to be pretty darn tough to improve things.