Nothing? Stop using so many plastic things.

Unless everyone changes, there's microplastic in your drinking water. The problem is so far along that even if we stopped all plastic products sale and manufacturing today, and actively worked to clean out all of the microplastic from the globe on an unprecedented level, we would still have microplastic issues by the time you die, even if you live longer than any human has ever lived before.

This isn't "it's hopeless and we shouldn't bother", it's more "there's more to do than can be done in anyone's lifetime, so try not to make it any worse".

It's good that you're aware and trying, you should keep doing that. Worrying about it all the time isn't really helpful. Just try not to unnecessarily contribute to the problem.