Use cwebp to compress webp images

cwebp -q 50 -m 6 -alpha_q 80 -mt original.webp -o target.webp

The above presupposes that cwebp is on your Windows PATH.

Where can you get this tool? Well, I found it here. I stashed a copy of the Windows version on my website here, and in my Microsoft Onedrive here. Oh, and also on my iDrive here.