This feature is only available in the desktop editor.
Select annotations you want aligned
You can select multiple annotations at once by holding down the SHIFT key while you click on different annotations.

Right click on the annotations > Align annotations

I don't seem to have control of the annotation that I want the others aligned TO. I have tried selecting 3 in top to bottom order and then right click/align on the top one... they all snap to the middle one.
What's the rule here?