Your code will be 01 because you will be appearing for Biology next year. Let's say if your NIOS exam is in 2021, your code will be 02. This is because through your highest qualification is B.Tech, your highest relevant examination which has Physics, Chemistry and Biology is not completed yet. So your code will be 02. Please visit the NEET information bulletin and check the page 17 of: https://ntaneet.nic.in/ntaneet/ShowPdf.aspx?Type=1F7D662EC0F41DE2013706728E830CBF545FD969&ID=D435A6CDD786300DFF204EE7C2EF942D3E9034E2