Finishing technique for gaps between the wall and the live wood we installed that shrunk
Most common solution would simply be caulk with a color matching the wood, not the wall.
Any sanding or harsh chemicals will damage the existing finish.
If you can apply without masking, you avoid risk of peeling off either finish. Choose a product for water cleanup if you doubt your skill.
Apply sparingly usually works best, you want people's eyes to ignore the gap not see a bold stripe of dissimilar material. Sometimes slightly recessing the caulking works well to trick the eye into seeing less depth. Start their and use it as backer if you need to bring it flush with the surface.
Backer rod helps in many significant ways, but carpenters usually omit.
Touch up those ends before you caulk, the unfinished wood draws attention.