Narita Airport Limousine Bus Shinjuku to Expressway Bus

I believe you have already seen this video: Shinjuku Expressway Bus Terminal - How to get around | Tokyo Travel Guide

It will depende on your reservation of the Airport Limousine bus. Some of them go straing to the Shinjuku Express Way Bus terminal.

Other Limousine buses from Narita will go to the Shinjuku Station West site. You just need to keep following the signs for "Expressway Bus Terminal".

Here are the timetables from Narita to Shinjuku:
https://www.limousinebus.co.jp/en/areas/detail/nrt/shinjuku/dep

It should be quite straightforward finding your way. If not, they have plenty of information centers where you can ask for information. People, guards and Konbinis (convenience stores) are very willing to help as well, so it is useful to write the name of the place you want to go in a paper and ask where it is. Or write "information center" on your paper so they can direct you to the nearest one.