Hopefully you’re skimming this guide before you’ve bought your supplies.
If you are using the Exynos (G950F) variant, then this particular connection between the mother- and daughterboards does not exist. There are only the blue and white antennae mentioned in step 21.
If you are in North America, you are likely using/fixing the Snapdragon (G950U) version of the s8, which is used in this guide. However, if you are outside North America, it will be worth checking which version you have, as you will need to purchase that specific daughter-board; they are not interchangeable.