Ah! I am gunna post your pic so people can see:

If a mesh part is slightly black like this then the normals have been flipped (it is inside out). As interior faces are theoretically invisible, they show as shadowed black in Blender. What you need to do is:

1. Go into edit mode and hover over the black part and press L, it will select the mesh part

2. In the left side menu go to “normals > flip direction”. This will turn your mesh around again and the shadows will be gone!