Finding out when self assessment started?

I have ceased trading and am trying to calculate if overlap relief is due. However I registered as self-employed over 20 years ago and can’t remember exactly when my business started. Can HMRC tell me what date I registered as self employed and when my first tax return was submitted?

Hi

Our self assessment telephone lines are closed until 4 September.  You will need to contact our self assessment webchat helpline, where my colleagues will be able to confirm if theres is overlap relief.  You can contact our webchat team at Self Assessment: general enquiries.

Thank you