My Shiny Garchomp won’t come out from underground after using dig. Should I be worried?

Only if it’s raining, if the hole is putting your home in danger, or if your garchomp is refusing food, @pokeking321. Otherwise, it seems that your garchomp has made itself a nest, which is actually perfectly normal for this usually cave-dwelling species. If, however, any of the above three conditions are true (it’s raining, you’re in danger, your garchomp won’t eat), then yes, excavation may be necessary. If you have another pokémon that can use Dig, I would advise you to use it. Otherwise, tie a rope to a small pokémon and give garchomp’s poké ball to it. Lower it into garchomp’s burrow and have it activate the poké ball to recall garchomp. Then, if your garchomp hadn’t been eating, it may be a good idea to take it to the nearest pokémon center.