Hi. Just find the product in your inventory, click edit, go the Keywords tab, and enter details into the Search Terms box. wait up to 15 mins. It should then go live.

I had a nightmare with this and after a load of back and forwards from seller support the only way I fixed it was to move the item to an entirely new category - its got something to do with the browse node/category or whatever other terms they can come up with. They also tell you (as you noticed) to look for it in the wrong place.

Sometimes its in More Details, sometimes its in Vital Info. I had to move mine to a completely different category, I kept trying to re-enter it into the category it was in and was supposed to be in, even dropping off a step or two. but in the end had to change it completely (ie from Stationary and Office Supplies to Home and Kitchen - mine worked in either so I ended up leaving it in Home and Kitchen)

Once I done that it was visable/searchable and sales started coming in again