The tool is designed to confirm if a UK National Insurance number is valid. But It can't valid NINO belongs to a specific individual.
The National Insurance number (NINO) is a number in the administration of the social security system or National Insurance used in the United Kingdom. The number also used for some purposes in the UK tax system. Sometime it is a "personal account number" in UK. The number is sometimes referred to as a NI No or NINO.
The format of the NINO number is two prefix letters, six digits, and one suffix letter. The example used is typically BN102966C. Often, the number is printed with spaces, like this: BN 10 29 66 C.
If you want to generate fake NINO, Here is a UK National Insurance number generator.