SBR doesn't allow to lodge tax returns without ABN, unless is a business intermediary who lodges tax return on behalf of.
Check if you need to lodge: Use the ATO’s tool “Do I need to lodge a tax return?”. If not required, submit a non-lodgment advice.
Ways to lodge:
Online via myTax (ATO Online)
Through a registered tax agent
By paper return (post to ATO)