Please see start of 'How do I submit my tax return using the ID checking system?' help article, but rather than completing it yourself you should follow these instructions:
If you're filing on someone elses behalf, when you see the QR code, you should click 'Other options' and then forward the link to them via email or text.
2. Fill in their email (or phone number if you choose the 'Text link' option), then click 'Send'

