If you’re having trouble finding items in a Calamity dungeon biome, you may have a problem with a biome chest in your Calamity Mod installation. You’ll need to uninstall the mod first and then install it again. This will prevent the biome chest from appearing on your map.
To install the Calamity Mod, you must have tModLoader installed. This is a program that lets you manage your game’s mods. You can download this program from the Steam store. You should install the mod on the latest build of Terraria.