Hi,
How do I modify the Principled BSDF in blender to fix the eyelashes when I export from CC3 to Blender 2.8.

Thank you

Hi
Try changing the Blend mode of the lashes from opaque to  "Alpha Blend" or hashed..or clipped.
also make sure you have the CC3 opacity map pluggin into the alpha port on the principled BSDF..not the diffuse texture
(see pic)

BTW, if you plan to render animated CC3 figures in Blender
watch this short 10 minute video on bringing unlimited face and body imotion clips from CC3 pipeline to Blender via Blenders action editor. 

RAG DOLL COLLISION ANIMATIONS FOR ICLONE 8 & 7
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Ghost Origins

My latest Feature length film created with Iclone.

My IMDB listing
Anabran Abdhul Quarnain - IMDb

Thank's AutoDidact,

I will test it based on your post