How do I fix the passenger side shoulder seat belt that won't retract on a 1991 honda accord ex.

Once the internal clock spring is released, the only fix is replacing the retractor assembly.
While this is a time consuming repair, the parts prices are kept low enough to encourage most to get the belt replaced rather than not.

The shoulder belt is what won't move. The lap belt retracts fine

Try cleaning the track with WD-40 and a rag.