Enquiries for NI number and tax assessment

I am an international student using UKVI to apply. I received the interest from the bank. I would like to know how to apply the self assessment for paying tax without any NI number (As NI number application being rejected by not having the work) . Also, I would like to know if there is any consequence to the BNO visa if not applying NI number (I.e. Staying in UK from September to now won't be count)

Hi Pam Diep,
Please refer to guidance at:-  Self Assessment tax returns
Thank you.