GSTR -1

YES u can amend such invoice 

if you mentioned b2b as b2cs in any return i.e. GSTR-1 you are free to amend any times . first you go to that table which you want to amend then mentioned gst invoice no of that particular month or year in case of b2b invoice . but in case of amend b2cs you are mentioned only month and then deduct the same amount from b2cs and add invoice in b2b in GSTR -1

Dear sir

can i change B2B invoice as (0) null.?

yes you can amend that invoice or raise the credit Note.against that invoice

thank you and congratulations