Sounds like you’re talking about a re-draw.
Taken from - https://www.bnz.co.nz/personal-banking/home-loans/manage-your-loan/top-ups#redraw
Get your extra repayments back
If you’ve made extra repayments to your home loan (on top of your regular minimum repayments), you may be eligible to borrow back (‘re-draw’) these additional repayments, without having to go through the full application process.5 The minimum amount you can borrow back is $3,000.
Unfortunately, you can’t do this if:
•you have a home loan on a fixed interest rate
•you have an interest only home loan
•you want to use the re-drawn amount for home renovations or construction that requires a building permit
•you’ve paid off a significant amount of your home loan through the sale of property
•the amount you want to borrow is more than the total of your extra repayments.