hey guys! So i use blender version 2.91.0 and i ran into an issue when importing the Mandy dress earlier. there's a black shadow around the shirt and collar and if this is happening to you, don't panic, you are not alone :) The newer versions of blender display both sides of any mesh as solid so if your mesh has been duplicated and the Normals are flipped, this may occur. To get rid of it, Simply go into edit mode (hit tab) hover over any black space, Hit L to select that area (repeat on other side or as needed) , and then hit the delete button or or the x button and VOILA! No more shadowing in eevee or cycles.
Alternatively, if you're a bit more advanced you can enable the alpha in the material tab and plug this node setup to the end of your tree (second picture) BUT results may vary (it worked in my view port but NOT in my render, i usually use this on the sims head since there's extra stuff there that shouldn't be seen and it works perfectly for that) I hope this helps and cleared up any confusion <3