“Dead” Sourdough starter?
Your starter can probably be revived. A bit of greyish to brown or yellow liquid on top is no problem at all just pour it off if it seems suspect. Most likely it is the hooch and does not technically need to be removed. I pour it off about once a week, when my starter is being fed daily, and stir it in the rest of the time.
A small amount of mold around the edges of the container is not too big of an issue, just pour out your starter and scoop about a tablespoon of “clean” (mold free) starter into a new container and feed.
If it happens to be really iffy, (is that a word) you can literally wash it. I took one I thought was a gonner, put it in a glass jar, and rinsed it off. Since the starter is pretty thick before you feed it, it will not dilute until you stir the liquid in, especially if you are somewhat quick about it. So rinse, swirl, pour and do it again if necessary. Then if you need to you can even take a small amount of the “cleaner” stuff and start to feed that as I mentioned before to be extra sure.
Next time when you’ve got a larger amount of some good stuff pour it out onto parchment paper and let it sit overnight (it will smell sour as it dries). In the morning you can pick up the parchment paper, crumbling the sourdough into little pieces and put your dried starter into a baggie just in case your active batch gets ruined.