You need official receipts to show that you have made a donation of $5 or more to approved donee organisations; such as registered charities, schools, and approved overseas aid funds (see IRD website for more details).
You need to complete and file a tax credit claim form (IR526) for the relevant tax year. To complete the form, you'll need:
Complete only the questions on the form that apply to you and attach all your donation receipts. You don't have to do any calculations. The IRD will take care of that.
Send the tax credit claim form to:
PO Box 39090
Wellington mail centre
Lower Hutt 5045
Download the IR526 form
Once you have filed your tax credit claim form, the IRD will send you notification of your refund amount within six weeks.