Enhance GLB Rig and Visemes

I have an existing character delivered in GLB format. The model already looks good overall, but its rig and visemes are holding it back. My highest priority is to get those two areas working flawlessly so the avatar performs naturally in real-time engines such as Unity, Unreal, or Blender... (Budget: €30 - €250 EUR, Jobs: 3D Animation, 3D Design, 3D Game Art, 3D Modelling, 3D Rigging, Blender, Character Animation, Character Design, Maya, Unity 3D)