If you stop working as a food delivery rider and no longer require your ABN, you will need to contact the ATO and advise them of the date that you stopped working as a contractor. In doing so, you will cancel your ABN.

Once cancelled, you will still need to include this Income on your income tax return after the end of that financial year (30 June). 

If you still require your ABN, you don't need to contact the ATO. However don't forget to include this income on your tax return!