I need to make a tooltip more accessible.
The first thing you can do is use the aria-describedby on the tooltip targets and use its value in the tooltip Id parameter to help screen readers. It is up to the screen reader to detect the change in the DOM and read out the new content.
This item is to add attributes to the tooltip such as role="tooltip", aria-live="polite", role="presentation", aria-hidden="false". The exact attributes will depend on more detailed research and may differ from what I have listed here.