Chances are, that's not mold - it's mycelium! Your kit includes an amended sawdust block with mushroom mycelium growing through it. The block may appear covered with a soft, white, mold-like substance. That's the mushroom mycelium, and it's totally normal and healthy for your mushroom block.
The mycelium of some species is more prominent than others. For example, Lion's mane mycelium tends to be finer and more difficult to see while oysters can develop into a very thick and leathery mat. If you are still unsure about what's growing on your kit, reach out to us with a photo and we will help you identify what's going on.
If your kit has black, green, or orange patches that could in fact be mold. It's possible your kit was damaged in transit.