Imported Blender Model and Separate Parts are Scattered All Over the Place

Hi I was trying to upload a model of a character I made in Blender I made some mistakes like the head not being a part of the body and some of the character’s accessories either turn invisible or is randomly placed somewhere where its not supposed to be in. How do I fix this or what tutorials should I search to fix this problem? because I have been trying to google what this kind of issue is called for am totally stumped.