1. If you already setup your myid on your smart phone + full strength, then proceed to step 2. If not, read here
  2. Go to this link https://onlineservices.ato.gov.au/business/ & login (prompt will be sent to the smartphone which has your MyID app installed)
  3. select the relevant business
  4. go to PROFILE > BUSINESS DETAILS > the tax file number can be see below: