They wouldn't "know" there's something to look at and that wouldn't influence evolution anyway. It's all random. When DNA replicates and am offspring is produced to create new DNA, sometimes random errors happen or change. Think like birth defects, except those are negative things and are detrimental to the new individual's survival. But if one of those random errors birthed an individual who had a beneficial "error" to them when they're surviving and let's them reproduce more, they pass on their "errors" more than other regular individuals. Since this living thing has an advantage in surviving and reproducing, eventually their "errors" will flood the population with this new trait. The thing is, when you're talking about like fish walking out of the water, it's all incremental changes over millions and millions of years to get there. You should check out the lung fish. It's technically a fish, but instead of gills it has primitive lungs and even some small legs. It's a prime example of the fish starting to change where after millions of years, their incremental changes are truly reshaping the animal from a full fish to one that has lungs and breathes air and can move slightly on land. But evolution in the end is random, and not all random changes are beneficial for the organism.