Do you mean an Identity Protection PIN (IP PIN)? If you don't have it, you can try to retrieve it by following the instructions at the following link on the IRS web site.
If you are unable to retrieve your IP PIN you will not be able to e-file. You can print your tax return, sign it, and file it by mail after completing it online. See the following FAQ for instructions.
If you file by mail it will take a very long time for your tax return to be processed. The IRS processing centers were closed for several months because of the Covid-19 pandemic, and they did not process any mailed tax returns. They are just now starting to reopen the processing centers, but they have limited staff and a huge backlog. On top of that, there is a delay for the additional verification that is needed when you file without your IP PIN.