Underpaid tax included in PAYE coding

Hi, I'm trying to fill in my self-assessment for the first time. There is section called "Underpaid tax included in PAYE coding". In the first page of this section, it describes what to enter as "Amount of underpaid tax for earlier years included in your tax code for 2022-23 (from your PAYE Notice of Coding). Please enter '0' if there is nothing shown:" It also says "If you pay tax under PAYE, your 6 April 2022 to 5 April 2023 tax code may have been adjusted to collect tax you owe for earlier years. Look at your 6 April 2022 to 5 April 2023 PAYE Coding Notice (P2)." I didn't get any letters about (PAYE Notice of Coding) P2. How can I get/see this information? And, in the second page it asks for the last tax year. I have no clue where to see it as well: "Amount of estimated underpaid tax for 6 April 2022 to 5 April 2023 to be included in your PAYE tax code for 6 April 2023 to 5 April 2024 (from your PAYE Notice of Coding). Please enter '0' if there is nothing shown:"

Hi cross_entropy

On your personal tax account on the PAYE tab there will be a link to view your tax code.
If you are unable to view your tax code online you can contact HMRC and we can check the entries for you Self Assessment: general enquiries

Thank you