Can losses be brought forward if they have not been declared in the previous financial years?

Losses cannot be brought forward if they have not been declared in the previous year's ITR or if it has not been filed within the due date. 

Any Loss under any head of income except House Property Loss cannot be carried forward to future years if the ITR has not been filed within the due date as per Sec 139(1). 

The assessee who files his income tax return after the due date mentioned under section 139(1), cannot carry forward the loss. However, if he still files a Belated Return with carrying forward loss, he will receive a notice under section 143(1)(a)(iii) i.e. disallowance of loss claimed in ITR. The assessee should rectify the error of the disallowed loss and file a Revised Return under section 139(5). Learn more about this in the following article. 

If the losses have been declared in the previous year's ITR, you can go to Quicko, click on additional details> brought forward losses, and bring forward your previous year's losses under the appropriate category of loss.