Everything Breanna said; also, this isn't healthy advice but in case of desperation.. breast milk is much sweeter than cows milk. You can try adding a sweetener of some kind, organic real maple syrup, davash (date honey/syrup) if you're starting honey now a bit of honey, or a vanilla syrup like Torani's etc.
Yes I definitely agree with Sarah! I use to add vanilla to my breastmilk when I had to defrost on some bags because the taste was slightly different after it’s been frozen.
I would say to start mixing the 2oz in the breastmilk if you haven’t already as you transition . Also yes maybe try warm to see how he takes it. For some transitioning periods it can take longer than others . If you just started keep doing what you’re doing & be patient .