To answer my own question, navigate is exposed through the reader object so the code below works. I don't think setSelectedAnnotations (or something similar) is exposed from the reader. Would be great to have that so this works `reader.setSelectedAnnotations([annotationItem.key])` (current error is `Error: Permission denied to access property "length"`)
window = Zotero.getMainWindow();
const reader = Zotero.Reader.getByTabID(window.Zotero_Tabs.selectedID);
reader.navigate({pageIndex: 0})