Blend shape mapping maps facial expressions to various preset shapes on your character model's face that represent each facial expression, eye blink state, and lip sync viseme.
1. Open your character's Unity scene and select the character in the Hierarchy pane.
2. Expand your character's root object by clicking the arrow next to it in the Hierarchy pane, if it's not already expanded.
3. Make sure the Expression Type is set to Blend Shapes.
4. In the Inspector pane, click on the Skinned Mesh Renderer referenced in the Mesh setting of the Avatar Model References component to find the object within your character's hierarchy that has a Skinned Mesh Renderer component with a BlendShapes list.
If your character has more than one mesh with blend shapes, drag the additional meshes into the Additional Meshes list under the main Mesh setting.
Note: Not all Skinned Mesh Renderers have blend shapes. If your character model doesn't have blend shapes defined then they will need to be created in a 3D modeling program such as Blender. Here is a short video tutorial for adding these in Blender.
5. For each expression found on the Avatar Model References component, click Add Blend Shape and select the corresponding blend shape from the dropdown list. You can click on the eye icon to preview that blend shape being applied, to verify you've selected the right shape.
Repeat step 5 for each expression to complete your face mapping.