How do I register as a Sole Trader

I already complete a self-assessment tax return. I am starting self-employment and can't work out how to properly register as a Sole Trader, as I am already registered for self-assessment. Do I need to have a business name as I am only working for one company.

Hi,
In order to register as a sole trader, you must register for Self Assessment.
As you have already registered for Self Assessment for another reason, you will need to register again.
The guidance here explains: Register as a sole trader
Thank you.