How to heat MAM bottle (the ones with vent thing) without using microwave

[Emmz0]

I've got some Mam bottles and use ready to use cartons of sma milk. How can I warm the mam bottles with the milk as they have holes at the bottom. Plus dont want ot microwave the milk

just stand it in some warm water. it has the soft plastic insert, so water won't get in the milk (though, if it did it wouldn't really matter)
if water could get in, then milk would get out!