Indian passport File number is longer than 12 digits, how to fill government online form?

Indian Passport File Number is longer than 12 digits - use last 12 numbers

There is a chance that your existing passport’s FILE NUMBER is longer than 12 digits .
The Indian government online passport form ONLY allows 12 digits to be entered.

In that case, enter the LAST 12 digits of your file number to enter in the online government form.

CKGS guidance for file number longer than 12 digits

This is an official response from CKGS to answer this question:

Let me know if you need more information.

NRI passport form FileNo field only accepts 12 digits

On government of India passport application form there is ‘FileNo’ field which has max 12 chars while the file number I see in my kid’s passport is 13 characters (numeric part).

What do we do?