When did my trading allowance exemption cease?

I'm filling out my self assessment form for the first time and I am doing it via the one that I can print out and send. There is one question which I don't know how to answer: When did you start working for yourself or when did your trading allowance exemption cease? I have to put a specific date into the boxes below but I don't know what to put. I started being self employed/a sole trader a few years ago but didn't earn over £1,000 until this tax year. Therefore do i put the specific date I earnt over £1,000 or do I put the date of the start of the tax year as when my trading allowance exemption ceased? Thanks in advance for any help/messages.

Hi Lydia,
Please put the date as the start of the tax year that you earned over £1000 as this would be when the trading allowance exemption ceased.
Thank you.