You have two choices concerning your RRSP Contribution receipts: If you have not claimed those contributions for deduction you may choose to claim them by adjusting your claimed RRSP deduction to a higher permissible amount (the lesser of your unused RRSP contributions for that year or your available RRSP deduction limit), or you may choose to not claim the contributions for deduction and forward those deductions for a future year.  

To correct the information on your prior year income tax return(s) you may either adjust the income tax returns for that/those specific year(s) using the CRA's "My Account", (see: http://www.cra-arc.gc.ca/changereturn) or by filing the form T1-ADJ (see: http://www.cra-arc.gc.ca/E/pbg/tf/t1-adj/README.html).  You may choose to correct line 208 RRSP Deductions claimed, and if you do not claim any or all the contributions you will correct the 'Schedule 7 - RRSP and PRPP Unused Contributions, Transfers, and HBP or LLP Activities" where you would report the contributions made and amounts that will be "Unused Contributions available to carry forward".