Your National Insurance Number (NINO) can be located either from your payslip, documentation from HMRC or by contacting HMRC directly.
If you do not hold a NINO but believe you are a qualifying UK resident, you will need to contact HMRC to obtain the details.
Use the link below to find your NINO
https://www.gov.uk/find-national-insurance-number
Use the link below to apply for a NINO