Select the text frame with the Selection Tool (V, Escape) and go to Edit > Copy and Edit > Paste. Manoeuvre this second text frame onto the left-hand page in a mirrored position. InDesign will provide pop-up guidelines once the text frame lines up exactly with the frame on the right-hand page. Once your happy with the positioning, select the Type Tool (T) and adjust the orientation of the text to Align Left from the Character Formatting Controls panel, as before.

I tried very hard to understand your request, but I still don't get it. When exactly do you want that your paragraph restarts at "A"? After a certain paragraph style (title, list or whatever)? In that case, you just need to create a multilevel list. Please be more specific, using screenshot of what you want to achieve at the very end. – Vinny May 18 '17 at 8:17 indesign-numbering