The idea is to enter your RRSP contribution that you used to make the repayment. Any amount from minimum repayment that you did not repay will be added as income on line 129:

Let’s say I have to repay $1200 to my HBP and I only contributed $500 to my RRSP that I can designate as HBP repayment. That means I have to add $700 on line 129. Here is how I fill the RRSP window:

If you leave the repayment empty(no RRSP contribution for this year), then all the 1200 will go to line 129.