How can I care for an ash tree that somehow was not affected by the EAB?

There are a few ash trees that naturally have more resistance to EAB than the rest. Some of these will survive on their own, but others may still get attacked by EAB, but just take longer to die. There are researchers actively looking for ash trees that seem to survive even after most of the other ash trees in an areas have died from EAB. They are called 'lingering ash'. Here is a website on that project - https://www.monitoringash.org/lingering-ash-info/. i would recommend continuing to monitor your ash tree. If it does start to show signs of decline related to EAB, you might want to consider treatments. As long as a tree is still relatively healthy, it can be protected from EAB through the use of systemic insecticides. Here is a resource that gives control options - https://hort.extension.wisc.edu/articles/homeowner-guide-emerald-ash-borer-insecticide-treatments/