Breastmilk unthawing & restoring?

🤱🏻mon • Baby Finn Born 10/6/17💙

If I take a bottle of frozen breastmilk out of the freezer, what’s the best way to warm it up? Also, if he doesn’t eat it all, can I put it into the refrigerator? I know I can’t put it back into the freezer.. I’m using it to make baby rice cereal so I know I won’t be using a full bottle from my storage. (He’s exclusively breastfed and we are starting to try solids today). He’s 6.5 months old.