Simple Gallery from CMS

Hi,
In this website’s home page it has a media grid section half way down.
We’re unable to update gallery lightboxes from the front facing editor, so I have to use the CMS editor instead. Can someone explain to me how exactly I can create one single gallery that pulls in multiple images from one collection area? I just need one gallery not multiple ones and for the thumbnail images to be evenly spread out, is this possible?

https://preview.webflow.com/preview/heads-up?utm_medium=preview_link&utm_source=designer&utm_content=heads-up&preview=ab919f77332a74657ad8439e45df04c7&mode=preview