Your understanding and thinking about of evolution is misguided. These changes aren’t conscious changes like how we are (hopefully) changing our energy usage to fight global warming etc

Evolution is a make billions of changes and see what still survives, those creatures with those changes that are still alive happen to have corresponding needs for the current environment.

When purple frog genetics trigger and birds see the frog better and eat it, those genes don’t get the time to continue to reproduce and spread

Humans and their adaptability and understanding of this concept this ability to understand how the process works in and of itself is the answer to your question. Our mental capacity allows us the intelligence to influence our environment and the knowledge to modify our bodies to fight diseases. On a more specific level we create vaccines that trigger responses inside bodies.

How organisms work is still being researched but we don’t evolve to fight disease we evolve and those who have the changes that happen to allow survival IN SPITE OF a disease are simply more likely to survive and spread their versions of genetics 🧬