https://all3dp.com/2/blender-to-unity-how-to-import-blender-models-in-unity/
Follow these steps to properly prepare the model for Unity:
1. With the model opened, in the right side-bar region, go to the “Transform” tab.
2. Set all the rotation axes (X, Y, Z) to 0°.
3. Set all the axis scales (X, Y, Z) to zero 1,0.
Once that’s done, let’s make sure the origin is in a useful position:
4. Select the “Cursor Tool” in the top left.
5. Select the new origin on the model by clicking where you want to place it.
6. Go to “Object > Set Origin > Origin to 3D Cursor”.
These last steps aren’t mandatory, but they can really save time once the model is imported to Unity, especially when importing multiple times.
Next, we’ll make sure all the model’s normals are pointing outwards, as some surfaces might be invisible in Unity if they aren’t oriented accordingly:
7. Go to “Edit Mode” and select all faces.
8. Go to “Mesh > Normals > Recalculate Outside”.
9. Save your file.
Now we should be all set to import the files to Unity. We’ll start by importing the native Blender file.
