Help with telling HMRC

Hello I recently registered for self assessment a few months back as I wanted to make furniture at home but it didn't go any where and I never made any money and just had a few small expenses so I did a final return and went back to job seekers. Now I have a job as a self employed courier driver but I don't know how to tell HMRC that my circumstances have changed. Do I need to amend final tax return. Thanks.

Hi Ryan Davies,
You will need to register as self employed for your new business.
At the tax year end you will receive your notice to file your Self Assessment tax return to declare the details. 
Thank you.