Wrong GSTIN mentioned in R-1

Sir/Mam,  With respect to just asked query titled —Changing wrong GSTIN in GSTIN

Pls clarify that as I file quarterly GSTR-1 , I should rectify GSTIN of buyer in GSTR-1 for July-Sept’20 quarter which will be filed on 31st Oct’20 ??

2)  The invoice no in which GSTIN  is wrongly mentioned is dated 18-1-20. As last date for availing ITC is Sept’20 return i.e. 22/24 th Oct’20.

So, If i rectify the said invoice in 31st oct’20, can the Buyer avail ITC of such Invoice legally as last date for availing ITC will be lapsed ??

3)  If i rectify the said invoice on 31st Oct,  invoice will get reflected in Jan’20 month. Am i right ??