@ Dolly what are reasons for defective return as per intimation ?
The AO may give the assessee an opportunity to rectify the defect within a period of fifteen days from the date of such intimation or within such further period which, on an application made in this behalf, the Assessing Officer may, in his discretion, allow;
So you have to seek extension under 139(9) only by an application to AO.
Section 119(2)(b) is not to be used for application purpose as it's not applicable here in 139(9) case.