How to set up an account to submit Self Assessment online?

Hi, I‘m a non-resident outside UK and not a UK citizen. I have an UK apartment with rental income. And I would like to set up an account online to submit SA and I have a UTR number. However, when I register an online account, it needs me to apply an National Insurance number which I don‘t have one. When I apply the NI number, it doesn‘t allow me to apply outside UK. Could you please advise how can I submit SA online outside UK?

Hi Kenjice,
Please refer to:
Register for Self Assessment if you are not self-employed
Thank you.