Here is a very short and clear instruction video on how to create a shape key/morph target in Blender 2.8. After this you would need to export as FBX and import the FBX to UE4.
Here is a very short and clear instruction video on how to create a shape key/morph target in Blender 2.8. After this you would need to export as FBX and import the FBX to UE4.