Since tax year 2013, you can enter the amount for RRSP deduction into line 13 on page 2 of Schedule 7. You may need to check the overwrite box beside line 13.
For tax year before 2013, line 10 of Schedule 7 is an amount up to your RRSP limit. This is where you need to enter the RRSP limit. however, you can choose to enter a lower amount for RRSP carry forward purpose.
For example, your RRSP limit is $2000, and you made RRSP contribution of $2000, however you only want to claim $1000 as RRSP deduction; you just enter $1000 in line 10, line 14 of schedule 7 will have an amount of $1000 to carry forward in future years.