Your earnings for that period will be in your tax return for the year 2021-2022. If you're submitting a paper tax return, the deadline is 31 October this year. If you're submitting your tax return online, the deadline is 31 January next year.
(Paper tax forms are horribly complicated because the form can't adapt to take account of your previous answers. So, for example, you'll be asked if your a company director or a share fisherman. Even if you answer 'No' to both, there are still loads of questions on the form that only need to be answered by directors or share fisherman and it can be hard to work out what you do need to answer and what you don't need to answer.
Online tax returns are MUCH easier though, as the form adapts to take your answers into account as you go along. I can complete one in under 5 minutes. So I STRONGLY recommend going down the online route).
If you've not yet
registered for self assessment (and for Class 2 National Insurance) though, you should do that as soon as possible:
https://www.gov.uk/register-for-self-assessment/self-employed