Overfeeding Baby- please help?

I've read through a lot of answers that are related to this, but I haven't found a solution. I mean my baby is a month old (was three weeks preemie) and is taking down 6 oz every three hours, sometimes wanting more in between. And yes, I try everything before hand. Changing, pacifier, swaddling, cuddling, playing, just walking around holding him. He started having a lot of issues having a bowel movement (he wasn't constipated just getting really upset) and a nurse said he's being overfed and it's hurting his intestines and to cut down his formula. She never said HOW I'm supposed to do this. I tried just giving him 4 ounces and now he just won't stop crying and I really don't know what to do. His app is in 2 days but that's just too long. I just need to know what I'm supposed to do.