Ah, your friend chose well. While it’s true that Alolan muk must be acclimated to cold temperatures (due to the fact that their bodies are primarily composed of actual liquid), they’re among the easiest pokémon to introduce to cold weather.
To do this, begin by keeping your muk indoors. If you live anywhere else but Snowpoint and if it isn’t winter, you can actually allow your muk to spend time outside for any length of time she can tolerate. Try to encourage her to increase the amount of time she spends outside little by little until she adjusts. If it is winter or if you do live in Snowpoint, however, the acclimation process should start by allowing her to wander about your home for any length of time she can tolerate, then withdrawing her into her poké ball to rest. Once she adjusts to your home, then she can move outside. Always watch for signs of freezing, however, such as spots on her body that seem a little stiff or the formation of frost. If you see any sign that she’s freezing over, immediately bring her inside and allow her to thaw by a heater or beneath a set of blankets.
Best of luck, anonymous!