So , I brought my character to UE, but the Mannequin shows up like this when I try to add the skeleton for it

Hello there @Eviee556!

This mesh/skeletion mismatch look a positioning problem. Make sure that all bones, especially the head, are in a neutral position in your 3D software. As well, check for any conflicts between the scale of the mesh and skeleton, specially if you were working with Blender, since it has a tendency to affect these values on export.