FORGET BILLS IN gSTr 1

Dear Sir,

I have forget to some invoice in GSTR 1 and In GSTR 3b for the month of Apr and Other Month in FY 19-20 So, its possible to upload all pending invoices in Mar return. my business related with E commerce and I have sale some bills in cash mode but I have forget to upload in GSTR 1 or in GSTR 3b